you are obviously just drinking too much for your system!!! please don't tell me you are even sick if you only have 2 pints?
unless you are allergic to alcohol i think this can be the only reason.
people have different tolerances, so even if you drink the same amount as your friends, for example, they might be able to tolerate it more than you. don't try and keep up with anyone else- drinking should be fun not a race...
you should drink more slowly and stop drinking as soon as you start to feel drunk, move onto water or another soft drink, until the last drink you had has managed to soak into your bloodstream. then if you still feel ok have another drink.....and definitely stop drinking altogether as soon as you start to feel queasy.
it's all about knowing your own limits. and remember the drink you have in your hand doesn't hit you untill 5-15 minutes after you drank it. control yourself, slow down and learn to drink properly, then hopefully you wont vom.