Hi Jatinder,
My understanding is that diabetics should follow a certain diet - in which they should sustain their blood sugar levels. Such a diet also helps to keep your weight in a healthy range. I will see if I can find you a link to a website that can give you guidance. A good idea would be to have a schedule for you meals and to plan your meals the night before. Having fruit such as apples, pears and bananas between meals will help with both your diabetes and in controlling your weight.
Increasing water, completely eliminating juice, drinking green and black tea and regular excercise (even increased walking) will help your thalassemia, your diabetes and any issues that you may have with your weight.
I hope this helps,
Sharmin