@wipergreaser and @mmmfood-
You guys are both in your late teens and are probably producing more anabolic hormones than you ever will again. Take advantage of that! You should be fine eating all the pizza and McDonald’s you want, but only if you’re active too. If you don’t play sports, you need to exercise. Lift weights. Go jogging. Take up a martial art. Force your body to turn all those calories into muscle. At your age, you shouldn’t be thinking about dieting, but you shouldn’t be wasting away on the couch either.
As far as antidepressants and weight gain, it depends on the drug and the person. I took one antidepressant for a couple years and it didn’t affect my weight at all, but a different one had me eating like a pig for the month that I took it, which naturally led to weight gain.