My DS was born 4 weeks premature and spent 8 days in NICU. While he was there he was feeding every 4 hours and then ondemand which was still working out to be every 4 hrs. I was BF but have recently switched to formula for several reasons. I'm feeding him aptamil but am slightly concerned about how much he's having, currently 3/4 scoops with equal water. He weighs 6lbs 5 currently and is 7 weeks. I've basically been feeding him what he wants... Bad idea or ok?