I have the same problem. Is this just when you race or everytime you run? Mine is every time I run and I'm only running a mile than it hurts too bad to continue. I was told in may be constipation but I took a laxative and that did not help. I have always been a runner, have tried more/less water and different foods as well as running any where from 1-4 hours after eating. Nothing makes any difference. If you find something that does work please let me know.