Upper extremity issues

[KnottedYet]

Sounds like upper trapezius and levator scapulae spasms. Those can pinch down on nerves and burn and cause some fab-o neural symptoms. (and they can kick off any nearby issues, too.)

do you have a physical therapist you work with? Might be good to have the help of a PT and to have them check your bike. (is this only happening on the bike?) Also have them check how your posture changes as you fatigue on the bike.

I wonder too if you are kicking in those muscles to hunch up the shoulder girdle to compensate to get some internal rotation/pronation to grip the handlebar. A PT who can really look you over might know if switching to an albatross-style bar would relieve that (by putting your grip in neutral plane.)

Since this is happening whether or not you have the Camelback on, I'd be looking at your body before I'd look at the Camelback; but it would be good for the PT to see how your body responds to the Camelback, too. (take it in with your bike)