Unless you run on a really short cycle, this is not a period. But that doesn't mean this is implantation bleeding. That's a rather rare occurrence and you're just as likely to have breakthrough bleeding. Really, you need to wait for a missed period because that's usually the first sign and you can test from there. Don't let things like ideas of implantation bleeding freak you out ahead of time when they're rare and not a sure fire sign of anything. And finally, I don't need to tell you that if you don't want to get pregnant, you shouldn't be having unprotected sex. Please protect yourself in the future if that's not your goal.

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.