Period supposed to start today/tomorrow

My hubby and I had sex Feb 14...13-14 days before my period. My cycle is usually 30-31 days long. I'm supposed to start today or tomorrow. Yesterday I really felt like I was going to...had that moist feeling down south that I usually get the day before I start. I had a VERY small amount (as in a few drops) of brown discharge yesterday. Nothing today...and no symptoms of Aunt Flow, either. I took two first response tests this afternoon...both very negative. Thoughts?