What Does Pain In The Upper Right Arm Indicate?

I am experiencing pain in my upper right arm (I m right handed) below the shoulder in the deltoid area. It s a sharp pain when I lift or rotate my arm. Little if any pain at rest. I can lift items without pain, but raising my arm or making sudden movements is very painful. I don t recall any sports or other incident that I can pinpoint as the cause (could prolonged work with a computer mouse be the culprit?). This has been going on for several weeks without getting better or worse. Feels like a muscle pull but isn t getting better. I m taking OTC pain meds (ibuprofen) and applying topical gels, with no appreciable effect. Any thoughts on what could have caused it and what I should do?