To update from last night/this morning, after getting like 6 hours sleeping in my wife's bed and using her pillow, my back/neck/shoulder feel pretty good. Not perfect, they're still sore, but not in terrible pain like I had been. And, that seems to have been the case the past couple of times I've used her bed/pillow as well. So, I'm thinking it's probably either my bed or my pillow that's causing the issue, or at least causing it not to get better.
I had actually gotten a new bed right around when the issue first happened - going from the twin bed that I had been using for like the past 17 years to a full-size bed. So, not sure if it's just some getting used to that. Her bed is a full-size as well, but mine is harder than hers.
More likely though is the pillow. She has one of those fancy $80 "Memory Foam" ones. Up until a week or so ago I was just using a couple of cheap cotton (or whatever) ones. Last week with some Christmas money I had gotten a "support" pillow for like $15 which at least has some support for the neck. But, I think I might just need to get a pillow like hers. No idea when I'll be able to do that though.
Blah.