Lol I cried loads (in private) when I left home and when my parents left me at uni first time. Cleared up fairly quickly after chatting to others and just putting yourself out there! Think it's just a bit of a shock to the system no matter how much you psych yourself up for going. It'll all be okay though!
I feel the same way mate, I want to go home so badly, but we'll get through it, give it a few more days, a week at most and you'll feel right at home, because after all home is where you make it.
I felt homesick after the first week, it just hits everyone at different points.
The worst thing you can do is spend time alone, you'll only make yourself feel worse. Go talk to one of your flatmates, even if they don't feel homesick yet at least you can break down that barrier of having someone you live with to talk to. Or if you don't feel like talking to them just sit in a communal area with them, you don't HAVE to tell them you're feeling homesick but at least being around someone else will help a little.