You could have a thyroid problem, and you should get that checked out to be sure.
You need to find a plan and stick to it. There are lots of things to help you. Atkins works wonders if you are willing to commit yourself (and no, atkins is not just cutting out potatoes and bread. Go to Atkins to figure out how to really do it) weight watchers, south beach, etc.
If you are eating right (and that is a very broad two words) and excercising regularly and not losing weight then ask your doctor for tips.
You could try eating six small meals a day instead of 1-2 or 3 regular size meals. This speeds up your metabolism. You could try atkins, it does work for most people, but you really have to commit and do it the right way. Otherwise, you will gain all of the weight back.
There has been a commercial on t.V late at night for I thing, relacore? It is for "people over 30, overstressed and overweight". I don't know how much it is or if it works, but you could ask your doc.
Definately make an appointment with your doc to decide what kind of diet is best for you and to test your thyroid. That would be the best route. Good luck!