I have had upper back shoulder pain for years. MRI can not detect anything. i feel the pain just above my breast as well. I have noticed that the side with the pain i.e the right chest side shows that my bone structure protrudes more than the left side.
You do CT shoulder, but this is mostly nerve stenosis due to cervical spine stiffness. X-ray and CT cervical spine should be done. Mammography also should be done to exclude any malignant swellings. You should visit your physician as soon as.