What Causes Inconsistencies In Periods After Taking Depo Provera?

i am a 28yr old female two yrs ago i got the depo provera shot i only got one shot becuase i had non stop bleeding from it since that one shot 2 yrs ago i still spot here and their between periods and sometimes have spotting only during sex. i never had this problem before getting the shot, could just getting only one shot mess me up that bad??