Bleeding between periods

So the last day of my last period was 2/25. I started my birth control pack as usual on 2/24. A week later, on 3/4 I started bleeding just a little. I thought maybe it was from having sex or even potentially implantation bleeding cause obviously the pill isn't 100%. Well for the last week on and off I've had varying amounts of light pink, red, or brownish red blood. My next period isn't due until next Thursday or Friday. I'm just not sure what could potentially be causing this. Any insight is appreciated.