Prolonged bleeding after Depo shot

Is it normal for me to bleed for almost two weeks after my first depo shot? From my understanding (well.. what my ob/gyn told me), I shouldn't have a period at all... Especially since I breastfeed. But for some odd reason, I got one a week after the shot and have been bleeding ever since. :/ This is probably all over the place, but hopefully someone can help.