Thanks for all the great replies.
Honestly, it just feels like I'm a bit off kilter, missing something. (I still think my newly-found inability to metabolize alcohol is really strange though.)
I started taking a multivitamin. I added a bit of weight training (which I always do in the winter), mainly body weight & dumb bells. Cut most of the alcohol out of my diet too. I do eat cleaner than most people. Maybe a cheat day with a gas station sandwich here & there.
As I get older, the cold really affects me too. I used to be pretty tough to running in the cold (including wearing shorts in some pretty low temperatures). Now, I'll back away from the door so easily at the thought of running outside.
I haven't experienced any real injuries to speak of [knock of wood]. I wonder if my willingness to go to the chiropractor at the first sign of something helps. Lots of ab & hip strengthening exercises probably helps too.
(I found single leg squats to be really important to my running health. If I don't do them, my back will tighten-up to make me walk like an old man...which means tons of stretching.)
The really sudden--almost overnight--weight gain shocked me! I'm now cutting even more calories from my diet & increasing my running frequency (as the temperatures increase). I think just cutting out the beer to once or twice a week is going to be huge.