I have been getting a stitch in my side since i was a little kid racing down the street with other (faster) little kids.
the answer is deep slower breathing. If you get stitches we are in the same boat. we never learned how to breathe "correctly" I have noticed that when i am on the Tandem with DH, and we are doing a serious hill, if i match him breath for breath I never get a stitch. If I am alone, sometimes i start to pant (shallow breathing) and oftentimes I WILL get a cramp.
If you can get a good yoga instructor to teach you to breathe, it would help.