May the Odds be Ever in my favor

Alright...so I cannot tolerate ANY birth control. Not only am I unable to take birth control but I am also allergic to latex. My boyfriend and I are sexually active (typically twice a week or so) and we use SKYN condoms. They are polyisoprene.

With the fact that we do pull out often, but approximately once or twice a month, I give him permission to finish in the condom. Also the condoms are never expired and he pinches the tip every time.

With the path that we are on, what are my chances of remaining not pregnant?