Depo Shot

I gave birth to my third baby on July 1st. I didnt want to get my tubes tied but I also didnt want to use the IUD or any other long term BC. So I got the depo provera shot on 08/25. I started spotting about three weeks ago which I thought it was my period because that was when I was supposed to get it. However, the following week I started bleeding. Its been 10 days, its not heavy but its not getting lighter either. I know the hormone will stay in my body for 3 months so I have no choice but just to wait. However, i just wanted to know if anyone experienced this while on the Depo shot and how long did it last? Its really uncomfortable and I'm even feeling cramps on my lower back plus other annoying symptoms. Ive gotten the depo shot before but Ive never experienced this.