The best remedy for diaper rash that I have found is:
Take 3-4 drops of mustard oil mix it with baby powder/talc to make a paste and apply generously on the rash and watch the rash disappear. Apply this at night and by morning you will see considerable improvement if the rash hasn't disappeared altogether.
The worse the rash, the more powder you should put in the oil to make it thicker as the oil on its own will sting. I end put apply oil on its on every night to prevent the rash from causing altogether. Don't put the oil on its on as it sting the baby buttocks, so I wouldn't recommend that at all.