Hey boomerang. This should probably be in In My Humble Opinion, which is where most medical advice threads go. I’ve notified a moderator so he can move it for you. 
Edited to add: Took me so long to write this that the mod responded before I finished! Now that’s service. Thanks, Colibri.
Now to answer your question, and no, IANAD. Just a person very experienced with depression, unfortunately, including both successful and unsuccessful treatments for it.
First, of course you should see a doctor (preferably a psychiatrist) in combination with a therapist, because it doesn’t sound as if you’re going through a brief phase of situational depression. At least, you don’t describe any incident(s) that may have caused or contirbuted to your current depression.
Second, to answer your question. Many antidepressants have “weight gain” as a possible side effect – in fact, I’d say almost all the SSRIs (Prozac, Zoloft, etc.) and the older tricyclics (Atavan, Valium) are often associated with some weight gain. That said, many of these same drugs *also *list “weight loss” is a side effect; pharmaceutical companies like to cover all their bases.
I can speak to my own experience that Elavil (amitriptyline) both knocks me to sleep and has given me bizarre food cravings that have, unfortunately, led to weight gain. I adore the sleep issue because I’ve suffered from insomnia all my life. On Elavil, I have literally fallen asleep in my chair in the middle of typing something. Almost every morning I wake up and find that the light by my bed is still on, indicating that I feel asleep before even turning out the light. It’s a pleasure.
The weight gain and cravings, however, are not. I’ve had an average sweet tooth all my life, though my real “poison” has been starchy, salty food (popcorn, for example). Ever since starting Elavil, I’ve found myself wanting to stuff fistfuls of sugar in my mouth. If I could have an IV drip of caramel I’d be in heaven!
However, despite the side effects, the medicine has gotten me through some rough times over the past two months. I doubt I’d’ve gotten through some difficult situations and made positive decisions in my life without the meds. But my psychiatrist and I are going to be tapering me off the Elavil onto another tricyclic that isn’t known for weight gain (can’t remember the name, unfortunately; even more unfortnately, SSRIs are out for me due to them causing a noticeable increase in my panic attacks).
Prozac, which I used back in the '90s, actually helped me lose weight, due to elevating my mood and causing me to rely less often on food as a comfort/numbing device. But in others it’s been known to cause weight gain. So really, it’s all a crapshoot. Work with a good psychiatrist – and as I said, be sure to get regular therapy as well, as drugs alone won’t necessarily get to the root of the problem – and hopefully you’ll find one, or a cocktail, that will work for you.
(Note: most docs these days are all about the SSRIs rather than the older classes of drugs such as tricyclics, I believe it’s mainly because the SSRIs are less prone to side effects, especially the groggy/soporific effects, of the tricyclics. I was only put on the older Elavil because as I mentioned, I have both depression and panic disorder, so we needed to find a medication that would help the depression without triggering anxiety. Not, alas, an easy task.)
Best of luck to you. I should have asked first: have you seen a doctor about the depression?
(BTW, anyone who just says “snap out of it” to someone suffering with true depression – not just a short-lived blue mood – should be shoved in a vat of molasses with a 100 lb weight yoked to his or her shoulders, with a recording of someone saying “your life sucks and it’s never going to get better” playing on a loop 24/7. Then let’s see how well he/she “snaps out of it.”)
