Diaper rash!

My 4 month old has extreme diaper rash out of nowhere. I’ve been using cream and a&d; but it’s not really getting that much better. Every diaper she’s had the past few days she’s been pooping, so maybe that’s the cause I just don’t know what to do I feel terrible but I know it’s not bothering her because she doesn’t even cry. I was thinking of laying a pad down and letting her have some naked time to air it out? Does anyone have any advice?