Balmex- You can find it at Walmart or Amazon. It has that zinc oxide and beeswax. It comes in a tube and you smear it on. My son had thrush which is a yeast infection in his mouth (white bumps)which caused the diaper rash at the other end.
The key is to find out what's causing the diaper rash. Balmex helps by acting as a barrier cream. Changing often and air drying is important.