Pain in right shoulder and armpit and arm, what could this be?

See orthopedist: Its important to establish a diagnosis. Shoulder pain could be from the shoulder or referred. Common referred sources include: abdomen, heart and neck. Shoulder sources include: arthritis, labral tears, instability, tendinitis, rotator cuff tears, bursitis, painful bony spurs etc. Therefore proper diagnosis is essential to stopping the pain. See an orthopedic surgeon.