My 1yr old developed a rash in the diaper area, including his penis and testicles, following vaccination. He's not itching from what I can tell, but it's not going away no matter what I use

It's been over 2 weeks and I've tried aquaphor, coconut oil, a&d ointments, and now we're using boudreaux's buttpaste max strength. It only helps by keeping inflammation down, so it's not red and irritated, but the rash is still there. I haven't the brand of diapers since birth and I change him very often, (too often if you ask my husband). Again, he's not fussing and doesn't even notice when I'm cleaning him, it's just unsightly.

Should I take him to the doctor, leave him in underwear for a few minutes after changes or continue treating with creams?