I think it might be an enzyme rash. <img src="i/expressions/rose.gif" border="0"> My daughter had this problem when she was a baby for a few months and then it settled down. Touch wood, she has had no problems since - she is now 3. We used zinc and castor oil as a barrier cream every time we changed her nappy. Also used a hydrocortisone cream 1% spread thinly every two or three nappy changes and this also worked great.
Good luck<img src="i/expressions/face-icon-small-wink.gif" border="0">
Good luck<img src="i/expressions/face-icon-small-wink.gif" border="0">