The causes of left back pain in women may be the following: 1. Note that it may be fasciitis, which is a sterile inflammation that occurs when cold, strain, or after exertion, and the pain is usually more pronounced. 2. It may be muscle strain, such as prolonged ambulation or low work, or some strenuous, relatively heavy physical labor, which may cause left back pain. 3. It may be intercostal 4.It may be a rib tumor or spinal tumor, or even a muscle tumor, which can cause pain.