More info needed there are multiple things that could cause it if you are really concerned you should talk to your doctor.
Your profile says you're 45... By that age you'd think you wouldn't have to ask that question on an advice site.
yeast infection, some sort of fungus- jock itch, crotch rot, POISON IVY if you have had sex in the outdoors.
Is she too dry? It could just be friction causing irritation to your skin. Try some ky lubricant.
Hair rubbing together could cause irritation or regrowth of hair if u shave
Or youre both allergic to the condom haha