am I pregnant? Is it my period starting?? Or is it implantation bleeding?

[Ilovepickles]

Me and my boyfriend have had unprotected sex a bunch of times and usually we are fine. We did it recently. I just got on birth control I think for almost 3 weeks I’ve been on it? And suddenly my discharge has started to change it was a bit of a yellowish color at first so I thought maybe it was an infection but then it started to turn brown then stopped. Since Sunday I’ve had brown discharge on and off and sometimes a little hint of red. I took a pregnancy test when I first noticed the brown which was about a week ago. And it was negative. My period starts in 3 days so is this me starting my period or could this be implantation bleeding? My boobs are starting to get sore but not half as much as usual. I’m very nervous please help me out.