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Have you looked into upper-cross syndrome? The only reason I ask this is because you describe symptoms very similar to a problem I had developed around this time last year. I spent almost 5 months (and thousands of dollars) trying to diagnose it and eventually was able to resolve it by addressing muscle imbalances with exercises, mobility/stretching. A good quicky test is being able to do a wall angle with your back flattened to the wall. They are also a (one of many) simple exercise to help aid in recovery.
It could also be tendonitis, but did you ever get an ultrasound to confirm the diagnosis? An impingement by the rotator cuff on the bicep tendon caused by UCS can give similar symptoms, but my ultrasounds came back negative.
As always take this with a grain of salt as I am not a doctor or trained therapist, but someone that had experience with pretty severe UCS and was able to recover through exercise and mobility work.
Let me know if you have any questions