Pregnant On Depo???

Okay so I've been on Depo since Nov 2016. My periods stopped completely on the sjot. Haven't had a period or even spotting since. About two weeks ago I had unprotected sex for like a week straight and my bf came in me. I've heard of people getting pregnant on the shot. Is this implantation bleeding? Reminder I've haven't had any spotting or periods since starting the shot. Please help.