Plan b help

got my period July 27th and on August 7th took plan b as a back up.  Almost two weeks later I started bleeding, not a typical period and it only lasted 3 days. It was a dark brown thick discharge. Not like a regular period at all. Typically my period lasts 7-8 days  I took a pregnancy test that came back negative.  Does this count as a period? It also came eight days earlier   Do you think I could still have gotten pregnancy