What Causes Murky And Blood Discharges?

I'm 19, female, and have been cramping constantly for the past few months, whether I'm on my menstrual cycle or not. I recently went onto Depo Provera, and after three weeks, I started spotting. I know that spotting is normal with Depo, but the colour and smell are very different. The colour goes from a dark murky reddish brown to a really bright red. It smells like normal blood, not menstrual blood, which concerns me. I'm constantly exhausted and am iron anemic.