what does it look like? If there are small white bumps it could be yeast. Using a product called Clotrimazole or Lotramin AF (both athletes foot creams- the active ingredient combats yeast and clears up yeast diaper infections very quickly).
If it is a very bad red rash, I really like Buderoux's Butt Paste.
If there are small clusters of white pussy looking bumps it is probably a bacterial infection and you will have to go into a pediatrition for it. What kind of diapers and wipes do you use? Probably stop using the wipes while your kid has such a bad rash. A wet wash cloth will not burn when you wipe the diaper area. Target brand diapers are the least harsh on my kids' butts (I use cloth now, but as far as disposables go these are the best I have found).
Hope this helps. Good luck!
at 10:40 PM on Jun. 26, 2011