Nappy Rash

Hi mommies!! My lo is turning 5 months and I'm experiencing his first nappy rash! What is the cause of it normally? We change his diapers every 2 to 3 hours , before every feeding session. Have been using mamypoko from birth and no change in formula as well. He has started eating cerelac since he turned 4 month so i don't know if it's because of food that he's been having rashes. Any way to treat a nappy rash & how to avoid it in the future? Thanks in advance🥰