I threw up but nothing came out. it's not a hangover, what should i do?

If it continues: see your doctor. If you are experiencing nausea that is interfering with your life (unable to eat, throwing up what you eat), that is not normal and a doctor needs to determine what is causing it to be able to effectively treat it. The fact you say it is NOT a hangover leads me to believe that you may be a heavier drinker, and that could cause gastritis or pancreatitis that can lead to nausea.