The pill is 99.9% or so effective if used correctly. So, if you were missing days or not taking it at the same time daily, its efficacy could have been slightly less than that.
It's just one of those things where it has been known to happen. Usually, it's due to one of the two reasons I listed above when it does but not always.
Hello, congrats and its possible that you became pregnant.
Are you on the pill or practicing another birth control method? As soon as you stop taking the pill or remove whatever BC you were using you can get pregnant although in most cases it takes a month or two. Also men can release sperm previous to ejaculation and it only takes one to become pregnant. The "pull out" method is not very good at preventing pregnancy because of this reason. Also some studies have shown that antibiotics can decrease the effectiveness of the pill. Congrats on your pregnancy. My son was born on your due date last year!