I used to get a side stitch on my right side when running. Granted, a bunch of things have changed (I've gotten fitter, different foods, different body water levels, etc.); to fix (or avoid) it, you might want to try switching from shallow chest-breathing (chest expands out when breathing) to belly-breathing (belly expands out when breathing).
You can practice deep breathing by lying back on a couch and putting a hand over your belly button. When deep breathing, your hand should rise and fall vertically. Yay for body hacks. ;)