Hello~I hope you are feeling better by now.
It sounds to me like a pinched nerve in your upper back and misaligned vertebrae, this can cause the issues you are having. I would suggest seeing a chiropractor, he/she will take an x-ray of your spine and neck, this will show any areas that are out of alignment and what they need to work on.
My dear mother had some issues with her breasts, I think it was a blocked milk gland, our chiropractor was able to help her and she didn't have any more problems after the adjustments to the areas causing the issue.
I hope you get the help you are looking for. God bless you.
Left sided shoulder and chest pain is often associated with Pericarditis, which probably sounds worse than what it is, at least in the acute presentation.
It might be a good idea to have this evaluated, even if it is only for your own piece of mind.
You certainly want to avoid any potential complications, if it happens to be Pericarditits, or to rule out anything more serious.