If the rash is persistent and looks like scattered. raised red dots, consider that it may be fungal. In that case you would need to use an antifungal cream like clotrimazole or miconazole.
My DD has had several rashes caused by yeast and we had to use a prescription cream from the doctor which cleared it up within 24 hours. Something to consider if it continues.
Othewise, I really like the Burt's Bees diaper cream. A mom friend recommended it to us and it worked when others did not. As a plus, I like the smell better than the purple Desitin. That stuff reminds me of dead fish.