Too soon???

I was supposed to start last Monday and I still havent started my period.. I took a pregnancy test Thursday morning and it was negative. Now, here it is Monday (technically, i know it is tuesday but i havent slept yet lol) a full week later and still no period.. is it too soon for a pregnancy test to work? My boyfriend and I had sex multiple times in the week before I was supposed to start.. theories? Advice?