TMI please help?!?!

Could this be implantation bleeding??  It started 2 days ago and at times has been a VERY light pink color. But has now turned into a brown color. My period is due on the 23rd and I took a pregnancy test today and it said not pregnant. I wasn't sure if my body has had time to get the adequate hcg levels or not. Also my period is always on schedule. It has been a very small amount of discolored discharge as well for the past 2 days. Any help would be greatly appreciated!!!