It is normal for your stomach to look bigger when you have your period. The reason is that when menstruation comes, it causes more tissue fluid in the body, which will cause weight gain and may look like there is edema all over the body, which will cause the stomach to be bigger. During menstruation, the blood vessels in the pelvis dilate and the uterus contracts, causing pain, which can also cause a larger stomach, which is normal. Before menstruation, there will be a continuous increase in progesterone, which will also cause the abdomen to look bulging. After menstruation, the progesterone will return to normal, and the symptoms will slowly subside and will not affect your health. Drink a lot of water during your period to speed up your metabolism and avoid a persistent abdominal bulge.