...Even with medical perspective, causes aren't always readily evident....
No kidding. As another old guy, I think I'm only a couple of months behind you. Doctor visits not helpful; scans and diagnostic work not revealing...what is the source of strange pains and functional difficulties that seem to arise out of nowhere? And cause lying awake late into the night?
I'm resigned to just accepting the aging process; very little seems to have been done to answer the complaints of those of us that are just getting older.
Good luck with the 'stretch and strengthen' discipline; in the absence of anything from my docs, I'm dedicated to the same program.