Help!!!!

We have started to use MCN's full time (had a week break after ds got a nasty case of gastro) and i cant seem to get on top of the nappy rash. He has had MCN on his bum for two days now since his poo finally settled after the gastro and already he has a red bum. I change the nappies every two to three hours as they are still new and im wary of them not leaking so they get changed often. Not sure what im doing wrong. He hardly ever has a red bum from disposables.

I was thinking of getting some cream for his bum but not sure what is best for MCN and also what is easy to get. Thinking this might work as a bit of a barrier which might help.

Any advice would be appreciated