I have tried searching but haven't found anything related (could be I'm not using search properly) so I hope I'm not duplicating here.

A year or so ago I had problems with cramp when training and doing races. It feels like really bad period pain and lasts about 10 minutes or so. I usually try and run through it but it isn't always possible. I went and had an ultrasound to check for cysts and other such things and was given the all clear (smears are fine too). It went away so I forgot about it but now it has come back. The pattern seems to be that it comes on within a mile or two of setting off when I'm pushing myself quite hard and often after ascending. Just ran a race and ended up dropping right to the back and wretching until it eased off. A few folk have suggested it could be due to drinking water just before running but it feels like its uterine not abdominal. Has anyone else experienced this and does anyone have any ideas what might cause it and how I could avoid it? Any help would be very much appreciated.