What Causes Abnormal Period After Missing A Birth Control Pill?

I started my period on Oct 31 and it ended on Nov 5. I started taking my birth control on the 6th but then missed about a weeks worth, then resumed taking them on the 13th. But took 2 at a time up until now, to get back on track. I noticed Sat night that I had started my period again. I have not had sex sinc I had my first period. Is this caused from the lapse in time from me taking the birth control pills? Could you please help me with this one?