“What causes shooting nerve pain in your back?”

Speaking generally, the nerves coming from (and to) your brain to (and from) your body pass through the spine. An issue with a spinal disc, or other forms of narrowed nerve pathways can bother nerves in the spine and cause various neurological symptoms, including shooting pain. You need a full exam and possibly a lumbar MRI to see if the source of pain can be identified, and then addressed.