Why haven't I had a hangover?

I'm a typical college frat kid. I drink a lot, and I've been drinking a lot more since its break, but its been about 2-3 years since I started drinking and I've yet to have a hangover. I've puked, blacked out, you name it all that good stuff but the next morning I just have terrible breath . Is it normal to not get hangovers even after blacking out and mixing all kids of drinks?