My period is 4 days late

Okay so my period is 4 days late tomorrow will be 5. I've had cramping here and there I think I may be pregnant. I have taken 3 tests already because I've been really worried but they've all said negative! I've never ever once been late for my period. I've been told that tests sometimes won't show up until two weeks late! Could I be pregnant and it's just not showing up yet?
I had  unprotected sex one day before I started ovulating he pulled out and finished but I've been told you can still fall pregnant off of pre.