I was on depo for 2 and half years... for that time i never got my period... after the 2 and half years i stopped taking depo but still didnt get my period for another 6 months. I wasent pregnant and there was nothing wrong... depo takes a lot longer to come out of your system then regular birth control.
Could mean many things. You body could just still be getting used to not being on the depo, or you could be pregnant, have an infection, be stressed and many more. If you're concerned you may be pregnant, then take a test or go see you doctor.