AF-like cramping during or after exercise

Maggie • Age 29. Baby #1 on the way!
Has anyone experienced this? Any idea what causes it?  
I just went for a run, and the cramps were intense. I am CD11, and I usually don't cramp much at all at any time during my cycle. It stopped after I cooled down. I remember this has happened in the past, but as I wasn't ttc, I brushed it off.