Susie,
You can also try leaving his diaper off for a while after you change him and let him "air dry".
The diaper rash ointment isn't suppose to make the rash go away, only protect it from getting worse. If his bum is still wet and you put the ointment on it locks the moisture in (making it worse). Make sure his bum is really dry before putting anything on him.Sometimes cornstarch or baby power will help but again he has to be super dry before you put it on. Even if all he has is a diaper rash, you can go to the doctor and get a stronger ointment for him if it doesn't clear up in 4-5 days. Poor thing! Good Luck!