Pregnant Scare

So, I had unprotected sex Oct 13/14th and according to my cycle...I should have had my period on the 28th but as I kept recording that it is late..I find that I have not had my period to this day. I was nauseous for a few days but my eating habits have changed to keep it at bay. I keep feeling something brewing up down there and it feels like I may be ovulating...help? No birth control..