Cramping in Vagina

My period was 2 weeks late and I was cramping down low, like in my pelvis and vagina. Well when it came on I was still cramping now I’m off my period and I still have mild cramping. I don’t have any weird discharge or anything, but my back hurts that’s why I’m thinking it’s a bladder infection cause I do cramp when I get one of those and I am frequently peeing. Which isnt like me, I don’t think I have an STD though, I do use protection every time with no incidents.