do try your best and stick to the right diet and exercise, my classmate was only 5'1'' and very obese, she thought she had no chance of having babies (they tried for 7years) then she lost about 40lb and she had a healthy baby, the natural way no IVF.
Check out some sites like diabetes.com or google 'glycemic index'. IMO, every low sugar option is better than full sugar one.
Good luck, you can do it
P.S.: It really works, I have 3 babies and I always became pregnant after losing a couple of pounds. I guess the body cleanses itself with the weight loss.