Try using a fragrance free dye free soap only, like summers eve brand soap,
Maybe you are irritated or allergic to the soap
Maybe your allergic to the condoms (if you use them) or even his sperm.
This happened to me twice and both times I dug around a lil and found a pubic hair stuck in there. Do you shave down there? That's when it happened to me both times.
I do shave, i thought that might be the problem. I stopped shaving for a few weeks but i kept getting the inflammation.
Also, i don't apply any kind of soap down there usually just wash it with warm water. But I'll try using the eve wash and see if it helps. I have also observed it gets worse after i use toilet paper, I've started washing it every time instead. May be it's just really irritated?
There's a possibility that you are allergic to condoms. I had a similar problem when I learned that I'm allergic to latex. My significant other now uses lifestyles skyn. It has polyisophrene in it instead of latex. I haven't had any problems since we switched condoms.