The same thing happened with a baby I used to watch over and first I tried treating it like a normal diaper rash. That helped but when it didn't go away I asked a doctor friend and he said it is most likely a yeast infection caused by the change in weather and moisture in the diaper which caused a normal rash to change. I treated it with the lotrimin but it can also be treated with women's yeast infection creams like monistat. It started going away within a few days.