it's called conditioned taste aversion. did you yak last time you drank? because if you did, your body has linked drinking to nausea and decided that you shouldn't drink any more, because it makes you sick and could kill you. evolutionarily, it makes a shitton of sense, you know, not eating/drinking things that could kill you.
but how to get over it? slowly accustom yourself to alcohol again, i guess. mixed drinks that don't smell too much, vagitinis like malibu and pineapple juice or apple smirnoff mixed with snapple apple or something.