Hi beginner
If you've recently made changes to your diet like increased calories and protein, you might be suffering from simple digestive pains.
When gases from the stomach can't escape (via belching and farting) they accumulate in the gut. This leads to pressure and cramping in the stomach muscles. If I were you I'd have a couple of good doses of bicarbonate of soda, to get it cleared from your system. You can by this from your local food store or pharmacy.
If the bicarb doesn't work - but I think it will - then it might be good to get checked out with your doctor. If you've got an infection or virus, it will require prescribed form of medication. However, it sounds very much like trapped gas to me.
When was the last time you had a bowel movement?
Craig