I recently moved to China about 5 months ago, and I have noticed my health steadily decreasing.?

I am a 25 year old male from North America. I was in relatively good health before I left for China, I am of European descent and not overly familiar with Asian foods. In the 5 months I have been here I have lost about 35-40 pounds. I wasn't that heavy before 6'3 210 lbs. I am constantly getting sick (colds). My stomach hurts 5 out of 7 days of the week. As of late I have become complacent to most things around me, as if I hate an don't care about anything. I have recently quit smoking, which should make me feel better I thought, but to no avail. I was wondering if there is anything I can try, like a diet change or something to help me out. Anything would be greatly appreciated.