spotting from being pregnant or plan b symptoms?

So I had my period on September 24th, and it was normal. Than when it ended I had unprotected sex and got my period again oct 3rd. Now I've had unprotected sex for almost everyday and yesterday morning I got all happy thinking I got my period but the bleeding was so light and only lasted two days now it's brown discharge. Could this be side effects of plan b like light periods or can I be pregnant ?