I agree with Totie. Antidepressants definitely cause weight gain, but so can an underactive thyroid. I would get the thyroid checked out first. If all is ok, then you may want to talk to you dr about possibly changing your medication to something that won't affect your weight (although to my knowledge, most antidepressants cause weight gain - and very quickly). Good Luck.
Sometimes the medications taken for depression cause weight gain. I would look into that and also the thyroid levels.
You are obviously hypothyroid. Get TSH, FREE T3, and FREE T4 tests.
The weight gain is key (as is depression). Funny thing is these docs will let us run around for years with a 4 - 5 TSH, and then when we get fat, tell us we're obviously stuffing our faces.
Take control of your own health. Get on thyroid meds, preferably one that contains T4 and T3. I was never able to lose weight on T4 only ($inthroid). Then monitor yourself with the above tests until you get to the correct dose.