Having horrible arm pain from my shoulder down to my elbow on my right side. what could be causing this?

Neck or shoulder: A pain that affects this area could be secondary to referred pain from the neck or a problem with the shoulder. Herniated disc, myofascial (muscle) pain, shoulder injury (tendon, impingement), etc could be the main source of pain. Only a good history, physical examination and imaging as needed will identify the cause. www.otwithmd.com.