I am on an ultra low dose 24 day pack bcp, take my pills everyday, and have been since Sept2009. I am currently on my 3rd out of 4 placebo reminder pills. I should be due for my period tomorrow. We had unprotected sex this morning. I also have my partner use the withdrawal method so he does not ejaculate in me. What are the odds that I could be pregnant? I was also wondering if what I'm considering my period tomorrow, could it just be withdrawal bleeding? And if it is, do I have anything to worry about when it comes to preventing pregnancy?