I'm having a pain in my left shoulder and it goes up the side of my neck... what could this be?

See a doctor: It could be neck or shoulder problem. You better see a doctor to get a complete check up.

Musculoskeletal: Neck & shoulder pain is most commonly musculoskeletal in nature, typically your trapezius muscle that attaches your neck to your shoulder. Perhaps you strained & injured it. Rest your shoulder by avoiding activities that make it worse. If you notice numbness, tingling or weakness in your arm, it suggests involvement of your spinal cord, eg pinched nerve. Go see your family doc for further evaluati.