late period

[yankeechic87.livejournal.com]

ok so my last period was in the beginning of june.
in the beginning of july i had sex and the condom fell off. the next day i took Plan B and the day after that as instructed by planned parenthood i began birth control pills (estrostep) which obviously made me skip my july period.

the problem is that tomorrow is my last day of placebo pills and i have not gotten my period this week like i was supposed to. last week i had some spotting and brown discharge. i took a pregnancy test on monday which came back negative.

my question is...should i start my next pack of birth control on friday even though i did not get my period? i have been really stressed and this was my first time ever taking birth control so i dont know if that has caused my missed period.

im really scared that im pregnant but i want to stop freaking out so much. i just want to know if it is safe for me to start my next pack without having gotten my period this month.