Hi Anthony
Although you're a bad case, I see these symptoms regularly in people who have problems in their ribs and shoulder girdles. I would suggest that you get these areas moving asap to reduce the tension and adhesions.
First of all, try a foam roller. Put put it horizontally under your upper back, on the floor. Bend your knees, lift your bottom off the floor and roll up and down your thorax. You may hear some clicking, which is fine; after a while you should also feel the area start to relax. Then you'll need a *good* physio to work on the muscles around your shoulder girdle, and to mobilse your thoracic spine, ribs and shoulder joint. In my experience, your shoulder is likely to be protracted (tilted forward) and this puts a lot more strain on the muscles and nerves in the area. For the muscles, they'll need to focus on your rhomboids, levator scapulae, scalenes and - particularly - your subscapularis. As your symptoms are also going so far down your arm, I'd suggest massage to your inner upper arm and forearm as well - essentially along the path of the ulnar nerve. I'd also get you gently stretching your forearm, elbow and thorax. There are some really good exercises for this in a book called Keep Your Joints Young by Sarah Key.
The key to this is to persevere. This issue has been going on for you for much longer than when you first started to notice it - these things don't just creep up on you overnight. How's your posture when you play bass?
Oh, and I'd avoid a collar. Immobilisation will make things worse.
Good luck!
Nell