Your body had the serotonin it needed while on the meds. You went off the meds, and now your body is seeking pleasure from anywhere it can to replace the "good feeling" the meds gave you.
I'm not saying you shouldn't have gone off meds, if you think that was the right choice for you then it is. I will tell you that the minimum amount of time to stay on meds is usually six months to a year AFTER you start feeling better, this will make the changes in your brain more permanent (i.e., producing and using serotonin). There are other ways to help you produce serotonin, though... exercise, vitamin D, fish oil... B vitamins, eating things like turkey and drinking warm milk (you can look up foods with tryptophan in them) will help, too.
I gained weight while on zoloft, and then even more when I went off of it because I was eating for comfort, which I had gotten from the medicine before. I didn't stay on it long enough, either, and I think that is why I gained weight.
