I suffer from anxiety, depression and bipolar disorder on top of anorexia. The first three I takes meds for and are stable. I am doing great. The anorexia is bad. But, the first med I took for my bipolar caused me to gain 30 lbs. and I freaked out. I begged my psychiatrist to try something else and he listened to me and I have since lost the weight and then some and am now in complete relapse but the point is that there are alot of meds out there. Maybe something else would be just as effective for you without the weight gain. Bottom line though is in order to lose weight you have to exercise and eat right. (funny coming from an anorexic). I found that I love stepping and use a step machine. There are so many different types of exercise, something has to work for you - just for a few times a week? I go through this with my husband. He wants to lose 10 lbs without dieting but wont workout. Hence, he remains the same.
Good luck,