My mother was experiencing this, as well as having trouble breathing in general. Even if she wasn't doing anything strenuous, she would start to get a shortness of breath and would feel like she was almost having a panic attack.
Eventually she went to the doctor and they told her that she had what they called small airways disease, which was causing the pain in her upper back as well as the trouble breathing.
All they could really do is give her an inhaler and tell her to be careful about not overextending herself.
It makes me really angry when I think about it too much, because she's never smoked a cigarette in her life, but she was exposed to a lot of secondhand smoke through her job in a bar twenty years ago and I think that is what has caught up to her now.