What Causes A Heavy Discharge After Menstruation?

I just got off my period about a week ago and i havent bleed at all since then, but this morning when i got up I had a light brown discharge, And now its a heavy brown discharge like a period. I use to take the depo shot but i have been off of it for about 4 months now or longer. Im just wondering what are some things that this could be, or should i be worried or is it normal? Thank you!