Hey ya,
i think that shot is diffrent for every one, a friend of mine was on it for a few years and when she came off it (as her mother told her its not natural for her not to have a peroid for 4 years) she fell pregnant with in 2 weeks (went to the dr 2 weeks after stopped to go on the oral pill but told her she was pregnant!)
but with my other halfs sister... She had one shot and did not have a peroid for several years.
I had it for 6 months and had constant ligth bleeding with it.. And I wont ever have it again.
Everybody is diffrent