First off i wanna welcome you here to YT and tell you that you have come to a wonderful place to find help. I am so sorry about your baby i hope for a speedy recovery. When my son had diaper rash really bad due to antibiotic and being I'll i put this stuff on him called aquafour( i can't remember how to spell it) you can get it in the baby isle with the other diaper rash stuff also what about Vaseline or neosporin my doc recommended that for my sons blisters on his raw bottom and keep the area where the skin is raw exposed to air to keep it dry. I'm not sure if you can use this stuff but maybe ask a vet and I'm sure they might have a cream to help to. Also clean him as soon as you see waist (I'm sure your already doing this) i hope i helped a little and if not I'm sure someone Else here will be of more assistance . Good luck sweetie AND KEEP US POSTED!
oh I FORGOT bout yogert it helps keep good germ fighting bacteria around mabe try that too.