could brown spotting be a sign of pregnancy , two weeks before period is due ?

Ok on 12-20-09 started period 12-22 I started BC (read online u can start during period) 12-24 BC was misplaced from nightstand by child , so on 12-25/12-26 I started again from a new pack (different brand) . On 12-30 my partner and I had unprotected sex and he came in me 2times that night , now on 1-5-10 I spotted brown for a few hours during the day and on 1-6-10 I cled a small amount and thought it was my MS (which is due sunday according to BC) and when I changed tampon it was again only a small amount of brown spotting ! Implantation bleeding , any input helps !