Always, always ask your gynae instead of others for questions like this because it involves your baby not others. And don't follow others because they have done it before bcos if anything were to happen they will not be held responsible. Our body are all different & our health also varies. Same goes to breastfeeding mums. Best is to ask your gynae/dr bcos they can access your health. Islam is simple & you have a perfect reason not to fast if you can't. Take care!