Baby allergic to diaper rash creams help!

So I’ve tried everything and he gets bumps and super red instantly I told his dr and they prescribed hydrocortisone and mupirocin and that made it go away but as soon as it’s gone n I use one of the powders or diaper rash creams or pastes the same thing happens instantly, his new dr says use Vaseline but the same thing happens with that too. The only thing that works is the mupirocin antibiotic but that’s not even a diaper rash cream n the dr doesn’t want to prescribe that again bc he needs to use a cream she says, n putting nothing to just let his skin breathe just results in the same thing bumps n redness everywhere n then he screams n cries from pain. I have tried literally every butt paste, cream, at the store I truly do not know what to do at this point. His skin is so sensitive