Pregnant?

My last period was august 14th, they ushally last a total of 5 days. I was due to have my next period September 15, and that night after sex i wiped and had little blood (what i thought was the start of my period, so i put a tampon on. (Tmi sorry) but when i woke up i took it out and there was no blood on it & I have not had any bleeding sense. I took 3 pregnancy test the past couple days and they were all negative. Im confused.. was that little blood after i wiped my period?