Why is age a concern? too young or to old?

Did you have any PT or possibly chiropractic before the injections?
If you had PT was it the same person or place , did you ask for a more advanced therapist?

Has there been any imaging - MRI or x rays?
What if anything shows on those?
If nothing specific stands out then it could be soft tissue related, trigger points or a nerve is being compromised somewhere.

Perhaps acupuncture might be helpful?
Or low level laser, also called by soft laser or cold laser..

Have you gotten other medical or perhaps even expert chiropractic opinions?

I found a teacher of PT that had his own PT clinic and taught at the local university, he was very good and did a full evaluation for my RSI/TOS issues.

You don't have frozen shoulder syndrome?