Hi Binita, congratulations for the baby. I can understand your concerns. I would like to know if your son is latching well at the nipple? He should be taking whole of the areola in the mouth and not just the nipple. In that case feed him at the breast first when ever he is hungry for ten minutes on each side. After that offer him the formula feed and let him take the amount he wants. Make sure to empty both the breasts. More the milk is emptied from the breast more it is secreted. Also night feeding is important as the prolactin hormone which is important for breast milk secretion is secreted at the night time. Take lots of fluid. As your baby will start getting enough milk he will take less and less of formula. I hope I have helped you. Thank you.