Implantation bleeding, going off birth control, pregnancy

I think that my last period began on October 14th, which would mean that I'm 10 days late. How do I know if what I thought was my period was really a case of implantation bleeding? Also, i went off of BC about a week after my period, because I was no longer having sex (I had sex about a week before my period in October) and experienced bleeding. I assume that since I had what I thought was a period, and then bled after going off the pill that I'm not pregnant. It doesn't seem possible that I could bleed after going off of the pill if I was pregnant, or is it? Does bleeding after going off of BC mess up your cycle? Could that be why my period is late? Help.