Only three weeks (:O), and you haven't got a plane ticket yet? :O (Then again, maybe I'm thinking from the perspective of Australia to China, as opposed to the much closer Philippines to China?)

I have no advice to give about homesickness, seeing as I seem to be incapable of experiencing it. But I would advise you not to let it stop you from enjoying yourself, as I've seen some people do (eg. one of my friends in Bordeaux made herself clinically depressed from being homesick :/).

And I would also recommend layers, with a big coat to go on top; you'll just have to get used to taking it off everytime you step indoors.