Help!

I'm nauseated all the time at morning and night. My period was brown. Every now and then I would get a pinkish color. Recently today I got a red color for maybe 30 minutes then it stopped and went back brown. I'm just so tired. And I really don't feel myself. I'm extra moody and everything makes me upset. I am on birth control but was antibiotics and had unprotected sex. I have taken 2 pregnacy test this month. I took one on this Tuesday and one last week. My period was April 17th and I ovulated May 2 and I had sex that day. My period was due on the 14th but it's been as described early. I'm not even sure this is my period. Could I be pregnant and testing too early, I keep getting negatives.