Could it be a possibility that it is a common side stitch, as i do hear that core strengthening and stretching can help prevent stitches, and by putting two and two togethor with your results it would seem that it could be a possibility. In my case it does infact feel like a stitch. I also seem to be improving by not giving into it, however i have just been walking and swimming at the moment (was even getting the pain while walking previously), will see how running goes in a few weeks after a few weeks of solid and regular core strengthening and stretches. Cheers 
