I suggest going to through emergency of hospital rather than urgent care. A few years ago I went to the urgent care in our area twice and they sent me home each time. Unless they see blood our you pass out they don't know what to do. Finally I went through ER at the hospital, which by that time I was peeing blood. It turned out that I had kidney stones and they took me right in. It doesn't sound like that's what you have but whenever there is pain it's not something to ignore. Go to emergency.

My son would have the same thing happen after soccer games, what the gastroenterologist explained to him is that there is this syndrome that occurs in some folks when they run for extended periods. The blood pools or is used moreso by the leg muscles, and this shift in blood flow will sometimes rob the intestines of their blood supply, even to the point of starving parts of the intestines for bloodflow causing little areas of necrosis, or tissue death, which is temporary and resets itself after the exercise is completed. However, the extreme abdominal pain comes from the fact that areas of the intestines are undergoing minute areas of necrosis and even though the phenomenon isn't too threatening in the long run, he was told to consider running shorter distances, or taking breaks thruout the soccer game to let the blood flow restore itself to the abdomen periodically. There is a name for this syndrome but I can't remember what it is.