why does my body suddenly reject alcohol?

22 M. i suddenly cannot keep down alcohol with food. on an empty stomach after throwing up, i seem to have no problems. i use to drink daily, but i figured some food might be necessary this time around since its been a while. i drank half a pint, 30 minutes after eating, and threw it all up after lighting a cigarette. an hour later and now im drinking the other half with no problems. im smoking cigs and shit. stomach hurts a little, but no nausea. this has been happening evertime i drink. where before on an empty stomach i would throw up after 2 pints. now with food and alcohol i have issues. does anyone know why or do you have a similar experienc??? thanks in advance