Is something wrong?

I used to be on the pill and couldn't remember to take it everyday and ended up with an ovarian cyst that is no longer there. After a couple of months I decided to try the shot. When I got the first shot everything was fine. My period went from being heavy and 7 days to being barely there and 13 days. On July 23rd I just got my second shot. It's now been the first time that I got my period after this one and I been bleeding since the 4th of August. Has anyone ever experienced this before? Is it normal when on the shot?