Pregnant from precum?

So I just started having sex like a month ago. My boyfriend and I just use condoms. Two weeks ago (towards the end of my ovulation like 2 days till the end) we had sex on a Monday (12/2/13). I guess I was in the mood at the time and didnt really realize what was happening, but when he put the condom on he put it on wrong like on the wrong way and so he flipped it around to put it on the right way. I think a little precum got on the top of it and that is what I'm worried about. (but since then ive researched and someone said that the semen in precum (if any) immediately becomes inactive if it isnt inserted directly from penis to vagina??) I thought of this however later on that week on Thursday (12/5/13) and ended up taking plan b on that Saturday (12/7/13) (5 days after we had sex aka the last possible day it may work) a week later (the next saturday (12/14/13)) we had sex again but the condom ripped this time. He didn't cum that night but I took 'my way' (another ec pill) anyways. My period was expected on tuesday (12/17/13) (yesterday) and now its wednesday (12/18/13) and I havent gotten it. I was told not to worry because the pills mess up the period cycle a lot but I am so worried which I have also heard messes up the cycle and may make me late but its weird bc my periods have never been abnormal. I just need advice