i thought period-esque bleeding meant you were definitely not pregnant. according to wikianswers, however, this is not so!
many women have experienced breakthrough bleeding, implantation bleeding, etc. that was much like a period through their early or sometimes their entire pregnancies.
which kinda makes me raise an eyebrow because i just had a two-days-late [i usually run like clockwork] disturbingly light cycle. but hey, i'm taking a test tomorrow. so we'll see.