Have you asked your doctor for suggestions? I'd hate to recommend something that might be counter indicated.
Have you considered water exercises? If you have a "Y" near you or a gym with a pool, most have water aerobics, etc. Might be something to look into, but still talk to your doctor first to make sure it's okay.
I have a tumor in my whole thigh and hip issues so I can't run or do much walking...
I've heard a lot of good things about Weight Watchers and although I've never tried it, I know that some people here have lost weight on it.
Do you keep a food journal? That's one of the handiest things because it lets you record and see exactly what/how much you are really eating, since sometimes, we tend to "miscalculate" the number of calories we take in.
I'm not sure of your medical issue, but a lot of us here have some type of medical problem, so maybe we can help you come up with some exercises that you can do. There are a lot of low impact things, if we know your limitations.