The possible causes of vague pain in the left side of the small abdomen in early pregnancy include: 1. abdominal pain symptoms caused by the stimulation of adjacent tissues due to the congestion of the uterus and pelvis after pregnancy; 2. abdominal pain caused by the enlargement of the uterus after pregnancy, which involves adjacent tissues and organs; 3. gynecological diseases such as endometritis, pelvic inflammatory disease and uterine fibroids before pregnancy, which further aggravate the original clinical symptoms with pelvic congestion after pregnancy 4. abdominal pain symptoms when suffering from urinary stones or infectious diseases of the urinary system during pregnancy. If the symptoms are obvious and not relieved after rest or accompanied by abnormal discharge in the vagina, you should go to the hospital as soon as possible to get a clear diagnosis.