Help!

Okay, so I'm on day 16 of my cycle (my last period ended 6 days ago) and I've had real bad back pain this afternoon, the type you get when you're due on. When I got home I discovered that I'm basically back on, like it was more than spotting!

I've had issues in the past and I've recently been told that I'm anemic...do you guys think I should be worried?