Implantation bleeding?

Has anyone ever experienced implantation bleeding? Did u test positive while it occurred? My period is always the same, heavy from start thru day 3 then days 4 and 5 and really light. I started yesterday with the brownish color and it's still going on today but no actual period. I've never had this happen before. I took a test this evening and is negative, but I'm also not due for my period for another 4 days.