Hey ladies!! So my baby boy has been on Similac Advance for about 2wks now and he's started getting really bad diaper rash lately and he spits up his formula almost everytime he eats.  He doesn't go back to the pediatrician until Jan 20th and I'm going to call them Monday and ask about maybe switching to a diff formula... My question... Some of his poops are really runny and he's very raw back there and sometimes cries bloody murder when your changing and wiping him... Any advice on how to know when you should change your baby's formula and if that can contribute to diaper rash too maybe if it doesn't agree with his tummy?