Are you relatively new to running?

I used to get those cramps, every so often, when I was a newer runner. Not sure if they were exactly what you're experiencing, though. They felt exactly like menstrual cramps to me - but would occur at any point in my cycle. They were painful enough that I had to walk through them. And take ibuprofen if I had one.

I once found discussion of this issue on a running forum - it was very helpful - lots of women appeared to experience it when new to running. But I couldn't tell you where that forum discussion was.