Hi a visit to a health professional might help determine the cause for the pain. If it happens with inhalation sometimes the difficulty is in the lungs. Infection could be there of various types, benign or malignant tumors can cause pain there according to some.
Sometimes things like food additives, drugs or alcohol are a burden to the liver according to some.
Problems with left shoulders are said to be from various things such as a heart difficulty or a nerve difficulty or a shoulder difficulty of various structures in there such as bone, muscle etc.
Tobacco may be a burden to the lungs.