Unable to drink alcohol?

I'm 17, and I think that as far as I can remember, I have never been able to drink alcohol without puking, most of the times just a few minutes after drinking. It's pretty annoying, I don't want to be the guy who says "nah I don't drink", and sometimes even just taking a swig and act like nothing will make me puke. What could be the reason? Please help, major bummer situation here.