Pain in the left side of the upper back and left side?

Upper back and L sid. There are many potential causes: herniated cervical or thoracic discs vs localized muscle strain vs facet joint irritation vs referred pain in particular from abdomen/diaphram which refers pain into shoulder/upper back. I suggest rest, antiinflam, localized heat, massage, pt and if not better consult md for MRI and consider epidural, trigger points injections, facet injections per md recommend.