maybe something you haven't thought about:

are you eating enough?

i have a really fast metabolism. if i don't eat, i start to get cold and weak. the weakness isn't so apparent when i'm at school, compared to when on the bike or lifting weights, but it's there with the coldness.

i joke with my friends: i don't get tired; i get hungry.

whenever i start exercising again, my metabolism jumps, and i need to eat more. perhaps you're going through a similar situation?

i suppose it's not too hard to check out. when you're in your office next time, and cold, try eating a bagel. see if it helps. digestion kicks out a lot of heat.