Stomach bloating can be from too high a level of sodium intake, which can cause the body to retain fluids (ie, bloat). I get this on long rides from drinking Gatorade, which has a higher sodium content that many of the other sports beverages. I have since switched to Gu2O to avoid the dreaded "Gator-bloat".

Stitches, or cramps, I get if I don't drink enough water. So I take a swig of sports beverage, & wash it down w/ H2O.