It could be thrush (possibly early signs of it- later on it may go pimply). I didn't realise the difference between nappy rash and thrush until a CYH nurse pointed it out to me- the normal nappy rash cream (sudocreme) wasn't doing anything to remove it. You can treat it with cream over the counter from the chemist- the one I've used is Daktozin. Worked a treat after one or two applications. And it won't hurt if it's not thrush to put it on anyway.