If it's not yeast (have you called your pediatrician's office?), Aquafor works pretty good!
You could also try to not put a diaper on him for a bit so his skin dries a little. We did that once with my now 21 month old when he had this horrible rash due to diarrhea... yeah, it made for a horrible messy night (changing sheets every time he went throughout the night) but his rash got much better.
Instead of wipes, clean him with water. I do that with my little one. I have a small container with warm water and I wet a kleenex... instead of rubbing/wiping, I dab and let the water run down. I do that until I get 'it' all. Then you gotta make sure you dry him very well before putting the diaper cream on.
Like the other ladies said though, make sure you call your pediatrician and see what they recommend. Maybe they want you to go in just to make sure it's not a yeast infection.