Diaper rash help!!!!! PLEASE HELP!!!!

My 15 month old son has a horrible diaper rash. It's even worse under his diaper. We have tried everything possible!!! What else can we try to help calm him for tonight. We have done every diaper rash cream known to be sold in stores. Letting it air dry. I change his diapers as soon as he pees or poops. I'll be making him an appointment asap in the am but he needs some relief tonight!!!

UPDATE!!!!!!

Thank you guys for the amazing advice! It's finally going away!!! Little man is actually walking around again!