Don't forget that diet (what you eat) is a big part of weight management. Generally when drugs cause us to gain weight, the mess with our appetite signals in our brain and we eat more without realizing it. You'll need to reprogram you brain to remember to eat less. I've had success with a food journal. I wrote down everything I ate, and realized what I needed to cut out (portions are the major thing here. Ice cream, cookies, etc aren't inherantly bad, if you eat a small amount. And eating too much of the best foods can still cause weight gain). Veggies are freebies for the most part, but I found I had to measure everything from ice cream (1/2 cup is a serving) to cereal (check the box) to spaghetti (a serving is much smaller than we expect). Use a smaller plate and eat slowly to feel like your eating more than you are.
I had a friend who gained a lot of weight from meds and couldn't loose it. Her doctor eventually gave her an appetite suppresant for a while and she was able to loose a lot of the weight. You may want to ask about that to help you get going, but you're also going to have to take charge again in thinking about what you put in your mouth.
Good luck!!!!!