Period came early on feb. 14 and was very light. Had unprotected sex on feb. 14&15. On feb.19 brwn discharg. In the last 2 weeks have had nausea&headaches, sore nipples last few days and backpain preg?

See a Gyn. Yes you could be pregnant. Take a home pregnancy test. However whether it is positive or negative you should see your gynecologist because of the abnormal periods. Take care.
Do a preg test! Most likely you are having some irregular bleeding. Do a preg test to make sure but if neg wait a few weeks to see what happens. If you r not using protection or are pregnant start a prenatal. If you have right or left sided abdominal pain just visit your obgyn.