i would have to agree with ducky. my cousin was taking the pill for a good while when she got pg.i have had my bc out since 9/2011 all the test i have taken come out neg but sometimes have pg like symptoms.a blood test is the best way to go.GOOD LUCK
Honestly, quite possible. The pill is only effective when used correctly. And it doesn't sound like you were using it right. You also need to be on it for a couple weeks before it takes full effect, so having unprotected sex the first day you get on the pill won't do much good.
However, it is also very possible you messed up your hormones. The pill, although very common and extensively used, is a drug. It can mess with your body very badly if it's not used correctly.
What you need to do is, now that you're not on the pill- only have protected sex, and take a pregnancy test. If it's negative and your period still hasn't came, wait another week and take one again. If the results are still negative and it's been 2-3 weeks late on your period you might need to see a doctor to get a blood test done.