Hi. I Was On The Depo Shot Four Years August

Hi. I was on the depo shot four years August 20th, 2015 I was suppose to go get my depo shot but I missed it. Monday night I saw heavy red blood as I wiped my behind so I put on a pad. Tuesday I put on another pad just in case no blood on pad but still when I wipe my but it's blood. Wednesday morning I got up to use the bathroom pad still on no blood on it, but as I wipe my butt it was alot of red and brown. What is going on?