Did you try to relase your shoes? Sometimes it they are to tight, a knumbness can occur from lack of blood circulation. Trust me, I have run more miles than most can count, with training for triathlons and cardio for my sport....
The other things could be problems with your heart, which you need to have a physician to check or lower back problems causing an impingement on a nerve. I would guess around your S4 or S5 region.