R.J.
If barrier creams like desiring are doing nothing for him... I would suspect a yeast infection.
My son was prone to yeast infections... Especially when his skin was broken (from diarrhea, or his allergy to wipes, etc.).
Diaper rash severe enough to cry over (come to find) is nearly alway a yeast infection. (Not just my kid).
You can use OTC yeast infection cream (also works as barrier cream), athletes foot spray (also works as baby powder)... But I preferred Rx'd cream when it got really bad. .