If you have done a lot of desk work /reading postures over many years, that can be why you have some of that stiffness & muscle tension.

If head/shoulders are rolled forward or hunched it can cause a lot of strain in the upper back/neck muscles, even trigger points that would need to be treated for them to resolve. A good PT should be able to assess posture and treat.

Might be good to look into some physical therapy, I'm surprised the dr that you went to didn't at least suggest trying that..