I'm trying to supliment my two month old with formula because I can't produce enough for him. But every time j put the nipple to his mouth with the formula he just screams and cries... My husband thinks it's just becuae his tummy isn't used to it and to keep feeding him with it even if he cries to get used to it.  but I think it's because   the type of formula im giving him. It's a gentle type of formula to help wih fussiness. Advice on what to do!?