Am I pregnant or is it the vitamins?

Okay so the day before yesterday I didn't have sex with my boyfriend but i let him put his manhood inside of me completely. I know that you can get pregnant from precum but the problem is he wasn't in me for long. Then this morning I wake up and took my One A Day Vitamins for Teenagers and I became nauseated and threw up a while after. My concern is I don't know if it was a side effect from the vitamin or if its a pregnancy symptom. Can somebody help me please?