I was on depo provera (medroxyprogesterone) and had my last shot december 2013, could it still be in my system? i have normal periods around the same time every month?

Depo-provera half-li: The half life of depo-provera when it is administered by intramuscular injection is believed to be about 50 days. That is why it is administered every 3 months. Your query states that the last time it was administered to you was in December 2013. Assuming first order kinetics that means approximately 610 days or 12.2 half-lives ago. At maximum you should have 1/1/4,096 of the depo left in you.