First Response

Hey everyone, my husband and I had an accident and had unprotected sex during my fertile week. We aren't even trying for a baby since our little guy is 14 months old. However, AF is due today, I have no signs of starting (usually I have bad cramps). I have been really tired last couple of days, starting to get headaches and have to pee a lot despite not drinking hardly any fluid. I seriously have only had a cup of coffee and a half a glass of water and have peed 4 times already today. I have taken First Response and am getting a negative result. Has anyone had bad luck with First Response? Those seem pretty accurate, but I just have a huge feeling that I'm pregnant.