I'm on bc pills but spotting for jus a day. is this a symtom of conception?

i had a miscarriage in aug 2010 and had a DNC done. ther after i'm on BC pills. Yesterday (2nd nov) i had spotting dark brown color(ive never experienced before). So i have a doubt if this could be a symtom of conception so from yesterday i stopped BC pills. If i'm pregnant i do not want to harm the baby with bc pills. Pl tell can one become pregnant even on bc pills? when can i take a hpt? My periods is expected on nov 16 (Prev periods oct 16). is it advisable to concieve immediately aft misscarriage?