Pain below the left side of the stomach is caused by constipation, proctitis, gynecological diseases, prostate diseases and other reasons, as follows: 1, in the lower left side of the stomach is the site of the sigmoid colon and rectum, when the formation of feces is mainly stored in these parts, people with constipation in defecation, because the nature of feces is relatively dry, so it will cause stimulation of the sigmoid colon and rectum, these people will be in the process of defecation, the The pain in the lower left side of the stomach, along with the feeling of bloating and diarrhea, should be alerted to the proctitis, the rectum itself is located in the lower left side, the colon connected above, the anal canal connected below, in the rectum when the inflammation, will release inflammatory factors, causing irritation to the rectal wall, causing discomfort in the intestinal wall, but also because the rectal peristalsis is hyperactive, so there will be bloating, diarrhea; 3. The actual pain in the lower left side of the stomach, accompanied by irregular menstruation and increased leucorrhea, should be alerted to gynecological diseases, such as pelvic inflammatory disease, endometritis, ovarian cysts, etc.; 4. Men with pain in the lower left side, accompanied by urinary urgency and painful urination, need to be alerted to prostate diseases, such as prostatitis, prostate hyperplasia, prostate hypertrophy.