Any fibre in your diet? Enough vitamins? Lack of vitamin C will cause constipation as will a number of other deficiencies. There are two less than obvious reasons for the gripes (gripping pains in the gut).
One is dehydration. You are taking in a lot of fluid to be sure, but protein requires water for its digestion and you may be shortchanging yourself on that score.
The other is that whey, milk etc contains a lot of calcium. Calcium and magnesium form a tight balance in the body, just like sodium and potassium do. Not enough magnesium in the diet will lead to cramps - its a classic sign. Redress the balance with Epsom Salts? Cheap and effective, or eat more leafy greens like cabbage etc.
Personally I recommend eating real food first and foremost. Failing that always, always on any diet (high calorie bulking, low calorie cutting, high carb, low fat, high protein etc etc) take extra vitamins minerals and EFAs as an insurance policy.
Hope this helps.