The possible causes are as follows: 1. It may be a physiological cause, as the uterus keeps increasing in size during pregnancy, causing lower abdominal cramps and discomfort. 2. It may be caused by some inflammatory diseases of the adnexa. 3. It is possible that the pain is caused by spasms in the intestines, accompanied by diarrhea and other symptoms. 4. It may be caused by hemorrhoids, with a feeling of swelling in the anus, causing lower abdominal cramps. 5. It may be caused by urinary stones, usually accompanied by soreness and discomfort in the back and lower back. If you have vague pain in your stomach in the eighth month of pregnancy, it is recommended to go to a regular specialized hospital to improve the relevant examination and give timely and effective symptomatic treatment after a clear diagnosis.