no other symptoms of pregnancy, Implantation bleeding?

Hello
I am kind of freaking out, which I tend to do when I get something in my head. I am on Gianvi and my last period was April 26-29. I take my pill at the same time every night. One night this month I took it 20 minutes late. I didn't think that would make a difference. On Friday I noticed a light brown discharge coming out and it's gotten to be heavier today. I'm a little confused. I've heard of implantation bleeding but I have no other symptoms of pregnancy. I am not due for my period until the 24th of this month. Is there anyone that can help? What could this be? I am assuming it's too early to take a pregnancy test, but I took one yesterday and it was negative. Please respond!