That is wonderful that you are able to go off medication for diabetes! You should be proud of that progress. I have Lupus and I find water aerobics is a great way to get in exercise that is gentle on my joints, but burns some calories. Just take baby steps in getting into an exercise program. For comparisons, you could pick a piece of clothing, or a belt, and see how it goes from fitting, to being too big. Its a good visual. You can also just take measurements once a month. A lot of folks find the loss of inches just as inspiring as the loss of pounds on the scale.
I don't use the GI diet, but follow Sugarbusters which is based on the GI. I really like the simplicity of it, and have followed it for a number of years. I have metabolic syndrome, and I am diabetic, so losing weight has been awfully hard.
I hope you find the support you need here.