What is causing my lower left side back pain?

Degenerative changes. This could either be from degenerative disc disease, a disc herniation or from degenerative arthritis. If this is significantly limiting and/or painful then you should seek attention for this from an interventional pain management physician.

Related Questions

What could be causing my lower left side back pain. I shift in my seat constantly to avoid it?

See below. Pain that occurs from sitting could be more than one thing. It could be related to your posture. It could be related to a painful disc which typically is more bothersome when people sit. See your doc for an evaluation. Read more...