I was thinking that it sounds like a fungal infection also. My DS3 had issues with a fungal infection for over two months. The only thing that worked for me was feeding him natural yoghurt and using the Daktozin cream to celar it up. Otherwise for a normal nappy rash, I swear by Disitin. Hope it clears up for you soon.

Also, if it is fungal, you will need to do an anti fugal and strip wash on your nappies to stop if from re-occuring.