please help me ?!!!

I'm on alesse 28 birth control and on my third pill pack. I'm a week before my placebo pills and started spotting with no sore breast which I usually get, my question is why am I spotting a week before and will I get a period ? I also have another question I had sex on 26 July with condom and he didn't finish at all and I don't think the condom broke so I took plan b anyways the next day and I got a small period six days after and then around my due day for that month I had a pretty heavy period so to make the story shorter I tested myself three times during august and beginning of September and they all where negative I had started the birth control on mid august and been ok with it but I'm wondering if they're still a possibility to be pregnant I didn't have any significant signs of pregnancy I am pretty normal and been getting a period about every month but only now the spotting made me worry! I'm asking if there's any possibility caust my grandma told me she would get a period during all her three pregnancies should I worry ? Please help me and I agree that I don't know much about these stuff I'm new to sex world