hi mummy! my LO is 2 weeks old and she is pooping after every feed which is after every 3hrs, similar as yours. recently i went to poly to check for her jaundice level and asked if her poop output is normal, doc mentioned that it is! for diaper rash, you may want to try Calendula Cream. it works wonders!
make sure his skin is dry and you air it before putting on new diapers again. frequency should regulate better though!