Hi,
I am sorry about my delayed response.
Unfortunately Avandia can cause some weight gain, and it sounds like you gained quite a bit. Losing the water weight should have helped some.
Have you met with a diabetes dietician? They can likely offer some good suggestions after reviewing your diet in regard to ways of cutting back/calorie restriction. You can also talk to your doctor about Byetta which may help with some weight loss, if you have no contraindications to use of the medication. There are also other prescribed weight loss medications(Orlistat,Meridia) that can help, along with a nutrition and exercise program.
Good luck and take care.