The left side of a woman’s lower back may be vaguely painful due to the following reasons: 1. It may be caused by lumbar muscle strain. Some women need to sit and stand for a long time or repeatedly bend over due to work, which may cause strain on one side of the lumbar muscles. This is because of some old injuries to the lumbar region, such as a strain of the left lumbar muscle or a fracture of the transverse process of the lumbar vertebrae on the left side of the spine. This is a condition that may be caused by fasciitis in this area. If the patient has had a cold or serious trauma on one side of the lumbar region, it may cause aseptic inflammation of the fascia here, leading to the above symptoms. 4. This condition may also be caused by some inflammatory diseases related to the urinary system and gynecology, such as when the patient has left-sided nephritis or some uterine adnexal inflammation, it may cause this symptom.