In pain on right side of body since mar 15. Just been told got thoracic outlet syndome. When I massage neck I get 10/10 head pain on right. Why?

See an osteopath. Outlet syndrome is tough, diagnosis of it needs precision sometimes surgical resection of a first rib helps. See your local osteopath for more help!
Occipital nerve. The occipital nerve exits the upper neck and travels to the scalp behind the ear. Pinching this nerve, by massaging, can cause pain radiating upwards into the scalp. However all of this takes place above where thoracic outlet occurs and should have nothing to do with it. Thoracic outlet impingement affects the arm and ?upper rib cage. A neurologist can advise you better, however.