If you are only taking the pills around the time you're having sex then yes. But if you take them as directed at the same time every day then oral birth control is around 99% effective. The last week of pills that are typically a different color are just sugar pills and you don't have to take them.
if you aren't taking your birth control correctly then yes you could get pregnant use protection and make sure you get you period as normal if you don't then take a pregnancy test