Left shoulder pain usually occurs on account of injury or sometimes disease. Shoulder pain can occur when the joint is forced out of its normal position. The shoulder joint is the area where shoulder blades and collar bones are connected. Pain that is more concentrated towards your left shoulder may also be caused by the muscles rubbing against the shoulder bone usually from irritation and swelling. Most commonly it can be triggered by painting walls, lifting heavy weights or suitcases, or repetitive athletic motions. However such pain can be symptomatic for other disease conditions as well. Here are few causes for pain in the left shoulder.
Upper back pain is the pain originating from the neck to the middle of the back. It is caused by a sudden injury or trauma, strain and poor posture. However the major reason for pain in the upper back is due to muscular irritation and joint dysfunction. The shoulder girdle is attached to the large muscles to the shoulder blade and the back of the thoracic rib cage. The muscular irritation in these areas is caused by overuse injury or de-conditioning.
The problems you are experiencing may be felt as a dull burning ache, or a more sharp pain that can be accompanied by a tightness of the muscles and a restricted range of movement within the upper back area. There are a range of other less common but more serious causes for pain in the upper back such as cancer, gallbladder issues (gallstones) or an infection in or surrounding the back.