I'm in need of some advice, PLEASE

My poor little DS has a tummy bug with diarrhoea and his tiny little bottom is red raw. I have tried all the lotions and potions I have for nappy rash (Moogoo MSM cream, pawpaw ointment, Curash, Brauers) but nothing seems to be working.

The best result I've got is from the pawpaw ointment. It seemed to be settling down this morning to a light red rash but it's came back quite back this afternoon.

I feel so bad changing his nappy coz he crys so much and is in so much pain, but I need to change him when he poops.

For anyone who's been through this before, can you please let me know what you used to help soothe your little one's sore red bottom.

Thank you.