Simple Habits which can cause Bloating
What Foods are you eating?
Food Intolerance and Allergies
Regarding menstural cramps: The hormone called prostaglandin. It causes the muscles in your bowels to contract. This is why you can have loose stools, diarrhea, and stomach pain when you get your period. (Source)
During the menstrual cycle there is a major fluctuation of hormones, namely estrogen and progesterone, and this causes fluid retention, swelling and the uncomfortable feeling of bloating. Women actually gain pounds of water during this time due to the ability of estrogen to cause fluid to be retained. (Source)