Getting pregnant on the pill?

I had unprotected sex 4 times with my boyfriend, 2 times last week and then 2 times on Monday again. 3 days later (today) later when I wiped I had a little bit of blood down there. I slept over at a friends house night before last and didn't take my pill on time yesterday, I usually take it around seven am but since I didn't have it with me I had to wait till I got home which was about 8. Could this be causing the bleeding? I'm supposed to start taking my period cycle pills in 3 days btw..