Suddenly i can’t have any alcohol

Does anyone have any idea what could have happened? I’m 19 (legal age of drinking in my country is 18) and I don’t drink often, but when I was drinking i could drink sometimes a whole 0.5l bottle of vodka or strong alcohol over party night and I didn’t even had strong bad hangover next day. But today I made myself one drink, a weak one, planning to maybe drink 3 or 4 and in about half of that drink i suddenly felt really nauseous and got bad heartburn. It’s second time i experience something like this, but last time it happened after much more than just half a drink.