I got mono in my late 30s while I was student teaching. I really, really couldn’t take time off - I only missed 1-1/2 days, but the fatigue held onto me for well over a year.
I’m not sure why the doctor isn’t checking her for mono. I would do that before committing her to two courses of antibiotics she may not need. Also, then you do know what you are dealing with and how to treat it properly. Just as a tip, if the swollen lymph nodes are toward the back of the neck (behind the ears) it is more likely to be mono.
I had mono in college - diagnosed when I came down with a nasty sore throat that turned out to be strep, and they did a blood test and diagnosed me with mono. For whatever reason, mono and strep frequently occur together - so the antibiotics may well be useful.
As far as I know, the only thing to do is rest as much as possible. I heard stories of kids who had to drop out of school for a semester because it trashed them so thoroughly; fortunately, I was fine within a week or so.
Look into topical numbing sprays or lozenges (assuming they even do anything; I’ve never tried them), oral painkillers. If it’s bad enough, a short course of steroids might be indicated - last year I had a vicious sore throat / laryngitis that made it difficult to swallow or talk. Nothing bacterial at play, but a short burst of prednisone made a HUGE difference.
We explained to our daughter how important it was to have plenty of liquids. We also told her that if she got dehydrated, she could possibly end up in the hospital with and IV line. Like most kids, she was not fond of needles, and had just had a blood test to diagnose the mono. We joke now about scolding her (not really) for not drinking enough soda or eating enough popsicles.
I got a form of mono in my 30s that eventually attacked my liver. At the height of it I was peeing brown, not because I was dehydrated, but because I couldn’t break down bilirubin so it was all coming out that way (and conversely, I was pooping beige, because the end-products of the breakdown apparently are what give poop its colour).
It basically passed on its own after a month or so, but not before a short hospital stay, which wasn’t necessary for what it actually was, but would have been necessary for other things that it could have been. Turns out when you’re showing symptoms of liver failure, “it’s probably mono, just rest and stay hydrated” is not the first thing the docs think of.
Thank you, that is good to know.
I will keep this in mind, thank you.
The doctor is calling in an Rx for prednisone. She is feeling worse. I took her for blood work this morning, in hindsight I wish I had asked the doc why we were waiting. She’s going to stay on the antibiotic until we get the test results but as of now, it isn’t helping. As far as I can tell, everything is pointing to mono. I hope the prednisone helps.
I’ve personally not had mono, but many of my college students contract it (so they are close to your daughter’s age).
Mono can vary in severity. I’ve had students who have to take a leave of absence over a semester to get healthy. And I’ve had students with mono who try and tough it out and drag their poor bodies through classes when they should be in bed.
All to say: try to lessen your teen’s responsibilities (like school – probably especially school) to allow for a lot of bedrest. It’s a nasty illness.
Hopefully the pred will reduce swelling / pain very quickly. I had it when I had laryngitis / sore throat from hell a year or so back and it made me feel hugely better within 24 hours. Actually, they may want her to finish the antibiotics since there’s such a strong co-morbidity between mono and strep throat.
My watch-the-color-of-the-urine advice was prudent advice for someone at home who is at risk for dehydration due to (in this case) decreased fluid intake.
Any hospital or clinic would do a quick and easy specific gravity on the urine, confirming some level of dehydration if present.
Your input has absolutely nothing to do with the OP’s situation.
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Yes, she is still on the antibiotic, although the strep is negative. We are still waiting for the mono results, so I think the plan is they just want to play it safely right now. The prednisone is definitely helping her.
When I got mono at age 30 (thanks, wifey), my doctor gave me an antibiotic for strep throat and I broke out into hives. Then he gave me a different type of antibiotic and I got a new set of hives on top of my original hives! My entire torso was a bizarre itchy red relief map. Then I went to the emergency room, waited for several hours after which they diagnosed me as having mono in about 30 seconds.
In my case, it just manifested as a sore throat and some general sluggishness for a couple of weeks.
I read somewhere, sorry I can’t site because I have no recall where I read it, that sometimes taking an antibiotic when having mono will cause some people to break out in a rash. I didn’t read anything about hives though.
That should’ve read I can’t cite not site! 
I got mono in high school. I did not get terribly sick but I went on a sleeping spree that would make Rip Van Winkle go “dayum dude”.
It was all I could do get up five minutes before the bus came. Throw clothes on, grab something to snack on, half sleep on the 45 minute bus ride, sleep in home room, sleep through half my classes and lunch, get home, go BACK to sleep, wake up long enough to eat dinner, right BACK to sleep again, rinse and repeat.
And I sure as hell didn’t getting kissing either. Thanks Mom (she worked in a hospital). Though maybe I should thank her…I rarely get sick and rarely is it bad…so maybe there is something to that a good immune system is one that gets a workout theory…