Rapid Weight Gain?

Two and a half years ago I was considered in good weight. (I was 18 and weighed around 115 lbs.) When suddenly I began gaining weight. I had been on an antidepressent (Zoloft) for two years prior to this weight gain..and still am to this day..but anyway. My thyroid was slightly out of balance (hypothyroidism) but was very quickly taken care of about 3 monthes after i began gaining weight. Despite the normalized thryroid, I still kept gaining weight. One and a half years after this weight gain began...I weighed 85 lbs more than i had (roughly 200lbs now). I'm still around this weight now. I know that there has to be something wrong with my body, but I (and doctors) have not found anything. I have been tested for Cushing Syndrome and Diabetes. My thyroid is constantly checked to maintain a good balance with my thyroid meds. So my question is:
What could be wrong that I am overlooking?My doctors have been puzzled over my rapid weigt gain for some time now.Could Zoloft caused this?

Have a sugar test as well as blood test looking for hormone problems. I have ploy cyctic ovaries and that made me gain a lot of weight quickly. It took two years for the doctors to even look at that. I hope that helps.

Zolof most likely is the reason why besides you eating alot, you have to stop snaking and eating foods that are not healthy, i have maintained my weight and i am on medication that could cause me to gain weight and i quit smoking also and i have not gained weight.