What Causes Missed Period After Discontinuing Cerazette Pills?

Hello, i am 15 years old. i have been on the cerazette mini pill for just under a year.. a month or two ago, i came off this pill and i have not yet had my period. i am worried i am pregnant, but even when i was on the pill i made sure i used a condom, and since stopping taking the pill we have been using condoms AND the pull out method. is this normal? is it something to do with coming off the pill or could i be pregnant?