I used to have a whole stack of J&J brochures with pictures of different kinds of nappy rash and I've thrown them all out grrrr! I was thinking it sounded fungal.

This is from my Miriam Stoppard book - hope this helps:

APPEARANCE OF RASH

Spotty rash that starts around the anus and spreads to the buttocks and inner thighs. You may also notice white patches inside your baby's mouth.

CAUSE AND TREATMENT

Thrush, caused by a yeast infection. Consult your doctor. She will probably give you anti-fungal treatments.

Does that sound like it? I would make an appointment with the GP but in the meantime, leave the nappy off as much as possible, clean the area with water, not baby wipes, and dry the area meticulously (no powder). You can go to the chemist to get a nappy rash treatment cream that is especially good for fungal nappy rash...I think it might be Desitin but not completely sure, would say so on the tube at any rate.

HTH.