Spotting for 3 weeks on depo

I had a caesarean section about two months ago.After this I had six weeks of light bleeding.I thought this was normal so I did not pay much attention to it. Six weeks after giving birth I decided that I would use the Depo Provera birth control method.About a week after getting the injection I began spotting. I was told that spotting is a side effect of this birth control method. I am currently experiencing my third week of bleeding which has gradually become heavier.Befrore having my baby I had normal menstrual cycle. I am breastfeeding, but my baby also gets formula. Is it possible that something is wrong with me orhas my mentruation just return and is a bit out of whack.