I’m always horniest right before I start. I consider it to be a general symptom of PMS - part of the irritability, which frequently leads to kissing and making up. I read in Cosmo once that sex is good for relieving cramps, so maybe that has something to do with it as well.
For a couple of years my period coincided with the full moon, but when I started on birth control it got out of whack. I didn’t notice any difference then to now.
You asked:
Well, be thankful you don’t experience estrus. It’s manifests as an overwhelming biological urge to mate with ANY male in the vicinity. If the only available male is your brother - you’re going to pounce on him without thinking twice about it.
Lack of estrus (along with the absence of external signs of ovulation) allows the human female to be much more selective when it comes to mating. This results in better control over reproduction and stronger family units.
I’m not sure when it happened, but my wild guess is approximately when homo erectus evolved around 1 million years ago. I would think it had something to do with why that particular ancestor of mankind was so successful.
My girlfriend also getts pretty damn horny on her period. It’s a good thing. Like you, she’s a whole lot easier to get to climax and she’s far more likely to try bold new sexual ideas. 
Hell is Other People.
My wife is the same way. The first few days of the end of her period is the ONLY time where’s she of the “shut up and just fuck me now” frame of mind. The rest of the month requires the use of my powers of persuasion. 
You’re horny during your period, my wife is as her period is trailing off. Perhaps it’s not fluid buildup. I vote for the testosterone-peaking theory. Some women wear testosterone patches (a controversial practice) to boost their libido, perhaps something similar happens naturally.
So… you’re having your period now… anything I can do to help?
bda: I’m not worried - just curious. And believe me, I do enjoy it
fuzzy-wuzzy: My breasts don’t always go up that much, but often they do. And they’re extreeeeeeemely tender. I usually have to sleep with a bra on, because if they move at all, the pain is so excrutiating I’d be up all night. And of course my cat decides that that’s just the perfect time to climb up on me and make biscuits on my chest - OUCH!
I think the kind of bloating that occurs in and around the abdomen is different than that which causes the breast tissue to expand. I don’t know though, so if someone does, please chime in.
JohnLarrigan: I am just howling over that one (wherewolf pun intended - hahahaha).
Milossarian: [bowing]Thank you. Thank you[/bowing] I just couldn’t resist the little teaser “Could it be just the stimulation of the warmth and wetness of what is going on in there.” I would say yes, except that I can almost always tell when my period’s going to start based on my degree of horniness, and at that point, I’m not bleeding yet. Considering the “talking-girl-stuff-comfort-level” of men, I do appreciate your input. Thank you again.
DrFidelius: “Be that as it may, there’s no reason for you not to enjoy yourself.” [blushing]I do enjoy myself, but not nearly as much as I would if I had a partner.[/blushing]
Gundhilde: Whew - another female chimes in in agreement. I’m feeling less and less weird now.
mega the roo: Most all of my girlfriends have told me that their breasts get bigger, too. I just don’t think anyone’s ever concurred with me about the horniness factor during menstruation. I’m really glad to know so many other women experience this.
missdavis102: I don’t have anyone to kiss and make up with, so that doesn’t apply to me so much (although maybe my body is acting as though I do out of some sort of natural instinct to do so). And sex is GREAT for relieving cramps. Any lower abdominal exercise is. From what I understand, cramps are caused by a constriction of the blood flow to the muscles in that area. Exercise increases circulation, relaxing the muscles, and decreasing cramping. I choose sex as my #1 preferred form of exercise
Sake Samurai: Thank you for the clarification regarding estrus and the evolution process. I am glad that we female humans don’t have external signs of ovulation. I do have to admit though, that when I’m as horny as I am during my period, were it not for morals, I would jump anything that came within striking distance. The urge really is that strong - I kid you not.
JoltSucker: I concur with your wife - that’s my attitude exactly! (See above reply to Sake) As for what you can do to help, where do you live?
I always just figured it took your mind off of it.
More corroboration on this front. I’ve been told that sex DOES comfort cramping (I’m more than happy to oblige). Also it is a fact that testosterone levels (as well as a few other hormones) peak during PMS and the early half of your period. Testosterone triggers menses, and is considered the primary sexual hormone so thats a likely conributing factor…as for why its set up this way, who knows. It could be coincidence, and since testoserone is peaking in all women at this time, why doesn’t it effect all women.
One theory to contribute: Are you on Birth Control? If so, sexual side effects are common with all pills I’m familiar with. So its possible that the change in hormone level affected by the pill could be the culprit.
Carry on.
My wife is the same way Shayna. Her GYN says its a point of peaking for hormones. A la pent up frustration in a hormonal sense. She also said sex during this time would be “astronomical” and we both now agree.
The GYN says its linked to having used OrthoTricyclene and its OD like effect on hormones after coming off of it. They can last up to a year and in some cases be permanent.
-G
My wife always loved sex during that time. Very horny, relieved cramps, etc. etc. It never bothered me in the slightest. Hey, I’m washable, what do I care? Now on to the ‘other’ subject.
Any one of you earned your red wings? Any of you women ever let someone go down on you while you were on your period? I never have, but a friend of mind has, and swears it was a night of mind blowing sex. I guess I’ll just have to believe him… my wife doesn’t have periods anymore. (One big plus to her hysterectomy)
I get horny toward the tail end of my period as well, although it can be somewhat unpredictable.
What I’ve always wondered, from an evolutionary POV, is why women and other female animals often become bitchy during their most fertile (PMS) times. Mares in heat can be dangerous, kicking and lashing out if you walk within 10 feet of their hindquarters. Female dogs (those bitches) get snappy. And we all know what we women can be like during PMS…“DO ME! DO ME NOW!” :::slap::: “WHAT THE HELL ARE YOU DOING?! DON’T TOUCH ME!” Wouldn’t that impede the evolutionary goal of successful reproduction?? I’d chalk it up to selectivity, but well…sometimes even the “alpha males” get that kind of response.
I personally do not like the idea of sex during my 2 heavier days…I’m achy, crampy, and feel like I stink, etc. Definitely NOT in a receptive mood.
I used to think the world was against me. Now I know better: Some of the smaller countries are neutral.
No answer, Just another I know where you’re coming from. that always seems to be the time of month my batteries run low.
If your head is wax, don’t walk in the sun.
-Benjamin Franklin
I believe it’s progesterone poisoning that causes this. I went through six years of off and on infertility treatments, and boy oh boy do I know alot about the female reproductive cycle.
From the time she ovulates until the day her period starts, a women’s body (if all is in working order) reacts as though she is pregnant. That’s why all of the physical changes take place - sore breasts, bloating, mood swings, etc. If you’ve ever been pregnant, you know that these are also signs of early pregnancy, they just continue and get worse for the first couple of months. And another thing that happens to many women in early pregnancy is that they get incredilby horny. I know I did. I’m normally the once a week type, but during those first few months, I could barely wait for my husband to get home, and I’d be all over him. I had wild fantasies about his boss, who also used to be my boss. I also had incredible dreams about sex.
Most books on the subject attribute this to the rapid rise in progesterone that occurs during pregnancy, but as I’ve stated, it starts before your period. It only starts to drop off the day your period starts.
How does this help the human race reproduce? Maybe it’s a bone thrown to the human male, to help keep him around at a time when his mate is really bitchy (no pun intended). I don’t know.
A lot of men say sex is great for cramps.
I was looking around in alt.binaries.test yesterday & found a picture of a woman on her period that I would be happy to post here to see if it stimulates anyone…
The reason I say it’s logical for a woman to be horny when she is fertile is because propagation of the species is very important ingrained thing or whatever.
(blushing rosily) Well, the same thing happens to me, and one of my friends suggested using an “Instead” menstrual cup during sex. It looks like a little tiny diaphragm, and while messy to remove, it does seem to hold back the flow so I can enjoy sex without grossing out my dear husband.
Prairie Rose
If you’re not part of the solution you’re just scumming up the bottom of the beaker.
I heard somewhere that women’s orgasms help slough of things inside there, you know what I mean? Maybe that’s got something to do with it. I always get super horny about 12 hours before my period starts and then again when it gets heavy… by my calculations, my period should start in about 11 hours… SOMEONE TAKE ME!! YES!! TAKE ME NOW!! YEAH BABY!
Meow
Orgasms cause uterine contractions, very helpful in expelling clots, which of course is the root of cramps.
Now, I can tell ya shayna, that it must be hormonal. I started those birth control shots, the ones that trick your body into not ovulation etc for months on end, and I have been unbearably horny ever since. Sex is almost all I think about. I feel like a horny 13 yr old boy who has discovered dirty books.
I would bet the hormones I am on for 13 weeks at a time are the same ones that cause your monthly …desires.
I’m not smiling at you…I have gas.
What ever happened to those touchy-feely computer peripherals. . .so people around here could get some relief? I thought they’d be at least in beta by now.
Ray (Maybe in Alpha?)
Omniscient: Yes, I was wondering the same thing. Since all women experience these hormonal changes, why aren’t all women affected by them in the same way. And no, I’m not on birth control pills. I was for many years, but haven’t been for almost 6 years now. “(I’m more than happy to oblige).” I’m sure you meant that in the general sense, but I can’t resist the urge to invite you over - especially given what I’ve just exposed about myself in this post re my current “condition.”
GigoloMan: I can attest to the “pent up frustration” thing. Abstinence will do that to ya! Sigh
Enright3: I love your healthy approach to sex during “that time.” Your wife’s a lucky lady. To answer your question; yes, I’ve done that. And I must admit that, like your friend, I found it to be the most incredible mind blowing sex I’ve ever had. Ever.
Ruffian: “Wouldn’t that impede the evolutionary goal of successful reproduction??” I would certainly think so. Much like wanting it most when we’re not fertile. Wacky biology, I guess.
psycat90: Thanks!
amberly: Great information. It’s nice to hear a success story regarding infertility, too. Congrats!
handy: Eeeeeeeew! Thanks, but no thanks, my friend.
Prairie Rose: Do those things really stay in place enough to prevent “spillage” during intercourse? Doesn’t all that banging around on it displace it in any way? I’m not sure if I’d like those, especially given that I couldn’t stand those tampons that don’t have an applicator. Not because I mind touching the blood, but because digging around up there trying to put them in and pull them out was a big pain. I think I’ll just look for a guy that doesn’t mind getting messy. Thanks for the tip though - it’s not a bad suggestion.
Meow: I hear ya! That’s what I’m going through right now. Eeeeeeeeeeeeeeee!!!
kellibelli: LOL - I’m loving reading about all these other horny females. And men think they have the market cornered on horniness - HA!
NanoByte: Now that would be interesting, wouldn’t it? Woo Hoo! Tech people - get on that right away!
Thank you, everyone, for all of your replies. I’ve found them to be informative, interesting and tons of fun to read! You guys are too cool 
“How wonderful it is that nobody need wait a single moment before starting to improve the world.” - Anne Frank