Hello ! how long has the pain been ? is it accompanied with any other symptoms like weakness in arm / shoulder muscles or loss of sensation in the arm ?
The history of how this pain started will play an important role in deciding about further investigation and diagnosis. Symptomatic treatment will include release of muscle spasm or trigger points in the muscles if any ( which I would generally expect in such a case ) and which is a cause of pain during movement , stretching of the affected muscles , taping to keep those muscles in the optimal function and exercises further on to improve muscle balance . your physiotherapist will be able to evaluate it differentiate between a muscular pain or a nerve compression from a discopathy . the treatment in either cases, starts with symptomatic relief of affected structures, with some advanced physiotherapeutic techniques in case of nerve or disc involvement. please go to your physio for an evaluation who will refer you to appropriate specialty if needed. Hope that helps !