8 days late and counting

As of today I'm 8 days late for my period. It has been regular for the past several years but I have also been on birth control up until 4 months ago. I have taken a couple pregnancy tests in the past week but they've all been negative. My fiance read that sometimes a pregnancy test doesn't read accurately at first because the HCG levels aren't very strong. Has anyone else had this happen before? How much longer should I wait before taking another test? We're TTC and getting really anxious to find out if we're pregnant or not but I feel a little ridiculous taking a test every couple days when they keep showing negative.