Diaper rash or something else?

Disclaimer, photo is TMI. I had my lo who is 8months na po ngayon on formula NAN infinipro HA 1-3years since 6th month niya (Iknow mumsh. Mali ang nabili na age group ng milk pero di namin napansin. Pero all good sya dun sa milk na yun. Hiyang niya) Then 3 weeks ago we bought a new can of NAN inifinipro ha 6-12months. and then when he poops, nagka allergic reaction po sya dun sa poop niya. Everytime na magpoop siya ngrred yung bum niya. Then we stopped giving him formula for a week and it subsided. Had an appointment sa pedia niya and she said it’s just diaper rash kasi pang allergy daw yung milk niya. Then we continued the formula. At bumalik ulit yung rash. Ganyan na. Prang mas malala pa. Sa tingin niyo mumsh, formula allergy ba? Nagkaganito na rin ba mga babies niya nung nag formula sila? Thank you! #pleasehelp