@littlesez it does clear up in sposies but within a day or two in cloth, he's sore again.
@NatB we have all sorts, Terries, wool, fitteds, wraps, AIO's and pockets. I've been using cloth for 4 years now so have tried most of the tricks of the trade to sort it but I think he's just got super sensitive skin and it doesn't like the dampness. He's also two andresisting changes so changing him more regularly would be traumatic for all involved
We've been in sposies since I wrote the OP and his bottom is so much healthier and Oscar is so much happier. It is sadly the right decision for us but if we have another baby then we'll be back to the cloth.