Menstrual-like cramps after exercise?

I’m not sure exactly where to post this, so I’ll take advice on that, too.

I stopped the pill last December and I was on it for 13 years, so needless to say I went through a roller coaster of changes coming off. I didn’t completely feel myself again (and my cycles didn’t level out) until July. Around that time I began to have intense menstrual-like cramps immediately following vigorous exercise (running hills mostly, but also occasionally after sex). They’re bad for about 10-15 minutes, worst cramps of my life. I have to either walk them off or curl up in a ball. It happens at all times of the month- before, during and after ovulation. There is no pattern. It’s always.

Does anyone else experience this? I have asked my doctor and an ARNP I work with (I work in maternal fetal medicine). Neither of them have heard of this before. When I google it I can find anecdotal evidence of women saying, “That happens to me, too.” But no concrete explanation.