Stomach Pain

I have been having a sharp pain in the left bottom side of my stomach when running. It is not like the normal "stitch" that runners get. Sometimes it gets so severe that I can not push through it, and the pain is still there when I start to walk. The pain usually only occurs during either a long brick or a tri, but recently it happened in the first mile of a run. Any help on what might be causing it or how to prevent this would be greatly appreciated.