Please help. Should I take a test?

I am on depo birthcontrol and lastweekend randomly started discharging a dark color or it could have been a little blood. But I had this everyday for only 3 or 4 days. I have been having really bad stomach pains.. And sometimes so bad I want to throw up. I have recently had sex a little bit before the discharge or blood without a condom. What could this be? Sick? Or pregnant? What should I do?