Hello, I am Dr. Selmani and read carefully your question. Some quick diagnoses for your problem are 1. Rib fracture , since it is related with breathing. That problem will go way in 4 weeks as the fracture heal. 2. Pulled muscle of the shoulder girdle. 3. More rare cause may be an herniated cervical disc that may cause nerve compression/ impingement that radiates along the arm. If the pain does not resolve during the course of 3 or 4 weeks I would suggest you to go ahead with more investigation with examination and consultation. Meanwhile during this time you can take pain killers such as acetaminophen and ibuprofen. I wish you a quick recovery.