Aww poor Em. I had the same thing happen with Noah, of course it had never happend before until I was changing his nappy in front of the MCHN. How bad did I feel.

First of all, I don't know if your using bum wipes or not but loose them for the time being. Warm flannels are the way to go. What sort of bum cream are you using? Bepanthen is great as a barrier cream, nappy free time is great too although a buggar with baby boys and the cold. Is there a way you could heat the room while has his nappy off? Are you using cloth or disposible? If cloth remember that they don't take as much liquid away from the skin, use nappy liners too and change more often maybe....

Other than that hun I don't know what to tell you. If it doesn't clear up in a day or 2 I would take him to the GP, it maybe fungal - thrush.

HTH