I'm on birth control and have been for a year. But this summer I've been kind of irregular in taking the pill (taking two months does side by side to avoid my period while traveling. Waiting two weeks after a period to start my next set). I am also on antibiotics, which I know lower the effect of the Birth Control. So last weekend (Friday night/ Saturday morning) I have participated in that activity bringing me to this page (he did not wear a condem). I was so terrified to be pregnant I went and bought the Plan B pill and took it the next day (Sunday). It is now Wednesday and I woke up in the middle of the night throwing up. Now I will be the first to admit I am completely ignorant in this situation, but could somebody please tell me what are the chances of me being pregnant.