What Causes Nausea, Vomiting Sensation And Light Spotting?

I Had Sex two weeks ago, i think i was fertile, and he accidently came inside me. I have been feeling really naucious and feeling like i want to throw up. I got what i thought was my period but it lasted from one evening to about 4 the next day. then stopped and didnt come back untill the day after that around 2. and lasted like 5 minutes and still is gone. what is the problem?