What Causes The Pain Inside Of The Vagina?

Hi, I've been having some vaginal problems. it's been going on for a while now and I've seen a doctor about it twice and they didn't find anything wrong. I have discharge that varies consistency and color. And it hurts to have sex. It also feels like im swollen up inside my vagina. im not pregnant or anything because i am gay and have a female partner. lately its also been painful to use tampons where as its never been like that before. mi also feel a little crampy around my uterus and just got off my period but there's dark brown stuff that comes out randomly. do you have any idea what could be wrong?