You could consider an EMG/NCV test of your nerves. This could identify if the disorder is radiculopathy vs thoracic outlet syndrome vs brachial plexopathy. A detailed physical examination by an experienced specialist (rare) can discern the disorder but an EMG test and/or a shoulder MRI can be helpful.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.