I assume you have talked with your doctor about it and gotten suggestions, but they haven't worked? The second thing to try because it's available and does work for lots of people is going to Weight Watchers. You aren't obliged to buy the food marketed as "Weight Watchers" meals in the freezer case to do Weight Watchers, it's a good program and has a lot of reinforcement if you go to the meetings and participate.
If the situation is really dire, like, if you are clinically obses, have you asked the doctor about weight-reduction surgery? (I would only consider that if my weight was really high, though. And even then, I'd try Weight Watchers first. I had a girlfriend who lost 80 lbs. using that system.)