Depo Provera

I've been on Depo for almost a year and a half and Ive never had a problem with bleeding until the past time or two i got my shot. Id have to get it like a week or two earlier than my normal window because I would get what seemed like a period. Now Im spotting and its only a month after my last shot. If Im bleeding could that mean its not working? And is there a reasonits started recently?