Just thought id post this as ive seen a few threads about nappy rash lately.
If you baby is very sore and it wont settle take them to see the health visitor or gp. My DD was very sore and even bleeding some mornings. I tried everything including boil washing nappies and even though i heard people talking about thrush i didnt think it could be that as it was just red.
I showed the rash to the HV last week and she said it was very bad thrush and i should of taken her sooner 
I felt so guilty but after 2 days the difference was unbeliveable, not a red mark in sight!!
She has to continue with the cream for 2 weeks but im so glad i showed HV when i did. If in doubt get it checked out!!