Confused

My boyfriend and I had anal sex on the 6th of January which was my fertile week, and he told me he finished in me. About a week ago, I have been feeling nauseous and having a lot of common symptoms of pregnancy. But this morning I took a test and it was negative. Not even a slight sign of the test being positive. I was expected to start my period on friday. But that hasn't happened. Now I don't know what to think. Please help