Someone did a post in the washing nappies bit about not using liquid in washing machines. it basically collectes up and goes minging
I would try taking the fleece liners out or not using ones with fleece in first. If that doesn't work then try a non-bio, like fairy or something to strip wash them and see if that helps.
Lots of nappy free time, wash bum with luke warm boiled water and my Nana also swears by sudocrem and no other nappy cream (She'll use vasaline in a push)
Some mum's use cammomile tea as a wash for bums, but I don't know if you can use that on a sore bum or not