There are several causes of left posterior lumbar pain: 1, acute lumbar sprain, may be caused by too much eagerness or force when turning, that is, flashing back; 2, muscle strain, strenuous exercise or violence may cause muscle strain, causing pain; 3, overwork or long-term incorrect posture will cause lumbar muscle strain, resulting in pain; 4, abnormal position of the uterus or uterine prolapse, can lead to lumbar pain, lumbago; 6, pregnant women as pregnancy lengthens, the load on the lumbar spine is getting heavier, 5. pelvic inflammatory disease, if suffering from inflammation of the tissues around the pelvic cavity, this will produce stimulation causing lumbago; 6. pregnant women with longer pregnancy, the load on the lumbar spine is getting heavier and heavier, sitting and standing for a long time may lead to lumbago; 7. having urinary system infections, such as pyelonephritis can also lead to lumbago; 8. lumbar disc herniation can also cause lumbago, mostly aggravated during exercise; 9. excessive intercourse can also cause lumbago Pain, but one to two days can be relieved, at the same time should pay attention to abstinence; long-term, severe back pain can not be relieved, the patient also need to promptly seek medical attention.