My 15 month old had a sore bum last week as he was teething and had bad diorriah

he wouldnt sit down or go in the bath it looked horrible and he screamed when i tried to change his bum.... everytime he has a sore bum i use cotton wool and water to do wipe his bum or put him under the shower if he has lots of poo i wanted to let him run around with his nappy of but because he had runny poos he kept doing it on the carpet in the end i bought him some little pants and let him run around in them and it seemed to get better...
xx