If you have a vague pain in your belly before your menstrual period, you need to rule out that it is caused by pregnancy, especially for women of childbearing age who have sex, and you need to improve your early pregnancy tests. After pregnancy is ruled out, the most common cause is pelvic congestion and edema due to changes in hormone levels in the body, and menstruation will occur in the near future after vague pain in the belly. It is caused by infection of the reproductive system with changes in vaginal discharge. Ultrasonography and gynecological examination can be performed to clarify the diagnosis and anti-infection treatment is needed.