I actually got pregnant while on the pill too... i missed a couple pills tho (dont know exactly when i conceived)
Ortho tricyclin lo was always messing with my cycle. A couple of days isnt that big of a difference however if your more than a week late take a test I too know someone who got pregnant off of birth control.
If you haven't started your period in a couple of days or so before you finish that pack then you should take a pregnancy test to be on the safe side before you start your next pack.You can get pregnant while on birth control it happen to me and my cousin and if the test is negative then your birth control might of messed up your cycles and then you should go see your doctor to make sure.
I too was on the pill.. & would start my period after the 1st sugar pill (or whatever the 4th week ones are).. i think usually you dont start your period until you stop taking the ones that stop your period from coming. Did you miss any pills that could have messed you up?