@Zaiten, yeah the cold weather isn't what gets me, it's just being in such a small space crowded with people. During the school year I'm sick a ton, but during the summer/other breaks I'm fine. Then when I get home from a con, I always get sick if I stay for more than a day. This past summer I only got sick once, right when I got home from a convention thing (non-anime) with a lot of people.
It's unfortunate but luckily I shouldn't really get sick anymore after I graduate this year.