What Are The Chances Of Pregnancy After Taking Ipills ?

I have taken birth control for over 7 years. I am supposed to start a new pack of pills this Sunday night. It is Friday night, and I just realized that I have THREE pills left (including tonight's)... which means I must have missed a pill somewhere along the way. I do not recall missing a pill though, but I must have! I have had unprotected sex throughout my cycle. Could I be pregnant? Since I have taken the pill for so long, by missing ONE pill am I still very likely to get pregnant?
Please help me, as I am very worried!