What Causes Stiffness In Neck And Pain In Shoulder?

Woke up with stiff neck 30 days ago. It has now escalated to my left shoulder with burning, throbbing pain, numbness. It has radiated to my upper back left arm. I can't stand the pain any longer. I finally took an xray 1 day ago (don't know the results yet).
Given prescription of tylenol and muscle spasm meds with no results. Female: 54 yrs old