That's a tough one - I would ask if there is any other medication that you can try that is in the same family of meds, but that may have less of an impact.  People, for example, react differently to anti-depressants, some of which can cause weight gain.  Steroids is a notorious - weight gain drug - it makes you retain water and seems to increase appetite.

When you say you've done the right eating - I guess I would suggest that you really make sure you are measuring portions, really counting calories, see if you can substitute fruit and vegetable selections instead of some of your more calorie dense foods and "increase exercise" as well.