Depo shot

I just want to hear some thoughts on it . I got the shot on day two of my period . The nurse today me to wait a week . Which was fine with me since I was on my period . That was the 10th , we got a bit carried away on the 21st . But days before I was having some cramping and brown discharge / spotting . And day off I was bleeding. I recently had my son two months. Ago this was are first time since than . I just want to know if the shot is affective ? And if the discharge and spotting is normal after the shot?