Contraceptive injection and periods?

it is perfectly normal to still have periods when your on the shots, there is no guarantee that it will stop your periods, i myself took the shot once and had just the opposite happen, i bled the entire three months and wound up severely anemic and my doc told me it was normal, needless to say i've found other methods of birth control. there is no guaranteed way to stop your periods at least not that i know of anyways. if your concerned with it or believe that your doctor may be wrong you can always request a second opinion, but everyone that i know that has been on the shot has still had periods.