Probably just a side effect from the depo. At least your not bleeding constantly like I did
I would talk to your doctor, just in case. I have never had the depo shot, but I had a friend who had it. While she did have the spotting, it didn't go so far as to continue until 2 months later. Call or go in to see your doctor, and see what they say. Its always better to be safe than sorry.
thats normal. When you do the Depo shot most females will not get a period and will get spotting. the dark discharge is just old blod that is still shedding.