False negative?

Is it possible I got a false negative? I tested on the 3rd day of my late period and it was a very clear negative. Now I'm 6 days late. Still no symptoms of it coming. Normally I have symptoms about 4 days prior to my period starting. My period has been really regular the last 2 years. Last night I had spotting after sex which has never happened to me. The spotting stopped right away though and everything went back to normal. Should I test again? Or is there another reason?