As I understand, you have pain radiating along your Left neck and shoulder, and may extend to the face. This can happen with chronic strain of the neck muscles, or with a slipped disc, and can also result from a combination of poor posture, lack of exercise and lifestyle (use of mobile/ computer for extended duration, stress), etc. Less likely it can result from any neurological problem. You need to consult an Orthopaedic Surgeon who will examine you thoroughly and may prescribe certain Xrays or even an MRI.