Chances of me becoming pregnant?

I take Ocella (Yasmin) and I have a bad habit of taking my birth control pills at irregular times.. sometimes missing them by a complete night and taking it when i remember the next day. Ive always wondered what my chances of being pregnant are. Im pretty sure its not 99% like it should be if i took them perfectly. Also, i have unprotected every single time my partner and i have , as long as i am on the pill. And those of you recommending me to start taking the shot due to my horrible memory problem, my mother wont allow it.