L.M.
This happened to my son also with amoxicillan... He was on his 10th day & broke out in a Terrible rash (No fever)... Took him to ER & they said he was Allergic to the amoxicillan!! I was shocked because he had been on the med for 10 days!! They said sometimes it takes that long to get into your system & cause a reaction.... They told me to give him benadryl & within 2 days the rash was gone...Maybe your baby has had an allergic reaction & your pediatrican may recommend another approach.. Blessings to you!! Aveeno cream is also wonderful!