Hello,
Your first line,
(I've had upper back pain near my neck for about 10 years that I let hang around, never testing or treating it. Also know, I've trained in the gym as a bodybuilding for nearly 20 years )
made me wonder about Thoracic outlet syndrome..
We have forum about that condition if you want to explore the sticky threads to learn more..
But some of your list of symptoms don't match up. But it also could be multiple issues..
You might use our search tool to look for injection or vaccination caused issues..
https://www.neurotalk.org/search.php

You might look into expert chiropractic for the neck , they can adjust more than only the spine.. Or expert PT or bodyworker.. maybe acupuncture?

Doctors have become so specialised that sometimes I think they don't see the whole person. Sometimes tests & imaging don't show a clear cause.