Implantation or Period?

I'm on the pill but have had a lot of unprotected sex with my boyfriend in the past couple of months. Up until this month I've been getting my period right on schedule, not a day late. This month though, a week after my period was meant to start, I got a small amount of bleeding, it was a brown colour and there hasn't been a lot of it. I'm just confused. I haven't had any symptoms of my period (usually I get bloated, really bad cramps, etc) and yeah I'm just confused. Do you think it's implantation or my period?