Cramping after orgasm ?? confused

I've never had this problem before masturbating but I was rubbing one out and I started cramping right as soon as I orgasmed or very close after it. I'm a virgin so it couldn't be related to pregnancy (that's the first things that popped up when I looked it up) and I've never cramped Luke this before after an orgasm. It was a pain in my pelvic region and I could feel it near my rectum too. And I don't really know how it compares to a menstrual cramp bc I don't think I've ever had one before but this is how I imagine they would be. But I'm about 12-10 days from my period so I don't think it related to that either. And penetration doesn't hurt or burn or anything weird like that so I'm just confused on what's going on.