Winter is a funny time to miss England, in my opinion. Or anywhere else that is wet/cold (e.g., Paris).

Odd about the Vitamin C - can't understand why fruits in China would have less of it than fruits everywhere else. Anyway, I don't know of any evidence to suggest that ordinary Chinese suffer from Vitamin C deficiency (exceptions might be the very poor), so why should foreigners here?

US Thanksgiving has no relationship to recognizing the spiritual significance of animals in any of the numerous different Native mythologies in North America or anywhere else. It is a celebration of one, perhaps not the best, variety of Applied Christianity.

Feeling weak can also be psychological, associated with the difficulties of psychological adjustment to an unfamiliar culture.

There's plenty of meat here and plenty of people eat it. I don't think a healthy local diet would cause your problems. Notice what most people eat, do likewise and you shouldn't have any problems. 2-4 months and the adjustment to altitude should be complete in virtually everybody. If you've lost weighty, eat more. I'm not sure about the effects of the air pollution, but these effects don't seem be be serious for most people over the short run - long run, I dunno. There's fruit everywhere, so I don't see why you would suffer a lack of vitamin C unless you don't eat much fruit. Lack of physical activity is pretty obvious - for those who don't otherwise exercise, trying walking a lot to wherever you have to go, &/or get a bicycle.