In my opinion, when a doc tells you you have to expect certain problems because you are "getting older," it's time to find a new doc
I have a similar problem--since I was diagnosed with diabetes seven years ago, my docs want to blame EVERYTHING on that; they never want to look for a solution. The ENT who eventually diagnosed my NF2 didn't want to run tests or anything because he said my hearing issues were a result of diabetes. I had to insist that he do the MRI that turned up my tumors. Fight for yourself!
As for the pain, I'm just under 4 months out of surgery, and I do have some problems with pain in my neck and shoulder on the side of the surgery. To be fair, I had whiplash as a teenager and have had trouble on that side ever since, but this pain is different. Mine happens when I get tired, so I have a built-in reminder to sit down and take it easy.
You said you use a cane--I'm sure that must cause some pain in the shoulder (and some other places, too
Have you changed canes or anything? I don't know, but it seems like a logical place to start.
Out of curiosity, what kind of surgery did you have when your tumor was removed?