Implantation bleeding?

Okay, so I'm not really sure where to post this. But the last two days (Saturday and Sunday) I've had light brown discharge and my period isn't due until Friday (10/21). I'm cramping so I felt like my period was coming but the bleeding never picked up and I don't have any today. Could this be implantation bleeding? I have 3 kids and I've never experienced this before. I tested last night and it was negative, so I'm not sure what's going on. ?