Answer: It could be a neck and/or shoulder connection problem.
The shoulder and neck work simultaneously. The neck has muscles that connect directly to the shoulder blade, the side, the front, and the back parts of the shoulder. The movements of the shoulder are activated by the neck and are controlled by nerves in the neck. Shoulder pain or dysfunction can be caused by problems in the neck and neck pain or dysfunction can be caused by problems in the shoulder. Examples of problems are sprained ligaments, strained muscles or tendons, impingement syndromes, or misaligned vertebraes. This can be caused by trauma such as a car accident, sleeping positions, falls, sports injuries, or poor posture.