If you miss 3 pills in a month...how high are your chances?

i'll be 19 in two weeks and i've been steadily taking the same birth control since i was 16 and almost never miss a pill. but i've been suffering some memory issues lately and i ended up missing 3 pills. (not in a row, spread out) i just realized this morning about the 3rd one. i'm due for my period in a week and a half. so... how likely is it that i would get pregnant? i've had a few close calls before but it never turned out that i was. i'm paranoid too cuz 19 is the age everyone in my family ends up getting pregnant! eek!