one thing you can probably start doing is some gentle work on correcting your posture - that alone might be a big help. The bad shoulder postures close down the area where those very important nerves and blood supply flow thru.

a very simple one is to lay on the floor- or bed if you prefer- and just place your arms out straight or at a slight angle away from the body {as comfort allows}
then just relax with diaphragmatic breathing { low deep chest breaths with full exhale -not shallow upper chest breaths}
and lay there for 15-20 minutes
if you can do that a few times a day you may see some tension releasing
or if you can do that easily you can move up to laying on a rolled towel {lengthwise under the spine} so that shoulders can gently drop back more and the chest can open and release at the same time.

And a xray should show if any c spine cause or extra cervical ribs that could be the cause or a part of the cause.

the nerve that affects the ribcage can get irritated too and cause chest spams/pains.

You might pick up some books or videos on Alexander technique or other bodywork styles - i found quite a few at our local libraries- the videos are really helpful for really showing what they are talking about.

I'm so chatty today LOL

PS- If it is very uncomfortable can you ask for some gentle PT at a very qualified PT clinic?
I had 2 advanced PT that did very thorough exam/evaluations {better than my docs did}
But if you do PT don't let them rush you into anything that feels like it will cause pain>
Do you get delayed pain- hrs or a day after use?