im 18 years old, i have been on birth control for about 4 years or so, i havent always been the best at taking it, i sometimes take 3-4 at a time. i havent gotten pregnant since ive been on it. i am on Ortho Tri-cyclen Lo. during sex, me and my boyfriend do not use condoms, and he often ejaculates in me. im not late nor am i due for my period but ive been feeling weird lately and i was wondering if it may be possible..since ive been on it for so long am i immune to it that its impossible for me to get pregnant until ive been off itt for a while? please help