Well I got pregnant while on the pill, and taking it at the same time every day, never missing it, so it is possible. But wait to see if you miss your period, then wait to take a test. If its negative don't hesitate to get a blood test done if you feel you could be pregnant.
Well birth control pills are not 100% effective so if you are having unprotected sex then there is a possibility esp if you are missing pills even if it's just 3. I would take a test if you are late for your period. If it is negative take another one in about 3 days. If it is still negative call your doctor to see what he wants you to do. Also were you on any antibiotics recently? Taking those can also decrease the effectiveness of the pill. Good luck and I hope everything works out for you.
When you skip pills or take a pill late there is always a chance of becoming pregnant. Usually there is a less than 2% chance that you can get pregnant when your pills are taken 100% correct. I think if you miss your period completely then you should definitely take a home pregnancy test.