I get this too, sometimes, not every time, it has subsided recently but it could just be part of the cycle. It is after about 1.5 miles of jogging and when I am toward the middle of my cycle. Anyway, I started looking into this by talking to my GYN about it. I have thick endometrial lining and she recommended a certain type of sonogram, which I scheduled, to look into any type of fibroids. I feel, though, like jogging could be just helping me regulate periods and hormones.

hey! I've been having this same problem--about 20 min into my run, I start to get kind of mild cramps, and after about 40 min, I have to stop/slow down a bit. Then, if I'm lucky, I can finish my run if I don't go too fast. It used to happen just periodically, but not it happens more often. It doesn't happen if I swim or just do the elliptical trainer. B/c I'm trying to get pregnant (and have been for over a year), I've been paying close attention to when I ovulate, and I've noticed it happens around the time of ovulation and near my period. I'm 1) annoyed b/c it interferes w/running, which I love; and 2) worried that it could be a symptom of endometriosis. I'm going to the dr in about two weeks & hope to get answers. . . If you get any info about why this is happening, pls post it!