something similar like that happens to me when Dave an I have sex....If I dont wash off immediately after sex I break out all over down there, and yes its painful. The doctor said it wasnt uncommon to be "allergic" to the ph levels in sexual fluids with some partners and that they change sometimes in a female and I could actually be allergic to MY own fluids. Its really bad if I've shaved recently and we have sex and I dont wash off with a warm wash cloth.
hopefully you're just fine!!!