Burning sensation after sex

Me and boyfriend have been having sex for about 7 months now, but about a month after we first started I got this horrible burning in my vagina. It’s just kinda throbs and feels kinda swollen. Now it happens a lot more often like sometimes for weeks at a time then it will go away for awhile and come back. It starts a couple minutes after we finish then lasts for anywhere from 1-12 hours. Does anyone know what this could be/ ever happened to them before? It’s very frustrating and I just want to enjoy sex again without having to worry about being in pain after.