Light spotting around the time you should start your period could just be implantation bleeding, it could be heavy enough that it could be mistaken for your actual cycle.
I know someone who had their normal heavy period every month while she was preg
I had my period for the whole pregnancy with my second child... It was weird but doc said is normal...
I had my period for the first 5 momths with my daughter. It is because your body doesn't produce enough hcg to stop the period.