How can I lose weight while taking antidepressants and medication for bipolar disorder?

I want to and have tried so hard to lose about 15 lbs. but I feel that my medications are preventing me from doing so. My doctor doesn't believe it is the meds. but the weight gain started when I began taking the one for bipolar disorder. I have had anorexia since I was a teenager quite a long time ago but I mostly have it under control now. I mean I have always been very thin and I have often starved myself if my weight went over 105 lbs. Many times I stayed in the low to mid nineties range and that is where I felt most comfortable. However as it is with anorexics I could never quite get thin enough. Now after many years of therapy I feel that I am somewhat better and more accepting of myself at a higher weight. I am not overweight according to the charts for my height but I very uncomfortable with being quite this heavy. Losing the 15 lbs. would still be in the healthy range for my height. But it feels impossible which is totally freaking me out because I have never had trouble losing weight. I am older now so I know my metabolism has slowed some but only 3 years ago I weighed 102 lbs. I have never really known how or been able to follow a diet plan very well. They seem to require you to eat so many times throughout the day and I am not hungry that much so I have to try and force it down. I only know starvation and that no longer works for me. I have tried just cutting back calories but still eating but I read that you should not go below 1500 calories a day. Is this true? I am not getting that many. I am wondering if somehow I messed up my body/metabolism from all the years of abuse with the starving or if I'm not eating enough (which makes no sense to me) or if it is truely the medications. Does anyone have any experience with or knowledge about any of this? Is there a diet that is easy to follow, works, starts giving results quickly and is not very expensive that someone can recommend for me? There are so many out there. Also I'd like to know even more about an exercise program/video with all of the same criteria listed above and that I can do at home and do not have to have a lot of special equipment. Please keep in mind that I have a slight knee problem that would cause too much pain if I participated in any kind of running, jumping, lunges or deep squats. If anyone is on these types of meds. and knows it is that which is causing the problem and that I am out of luck, please let me know that too. Thank you for any and all help and advice you are willing and able to share.