Depo provera side effect?

Been on the depo provera shot for about 9 months and I had my 4th shot on June 6th due another on August 29th, I had bleeding trouble for a long time which finally stopped the end of may. Wednesday night I bled a little, around enough to fill one pad but I didn't bleed at all through the day, Thursday night I bled again and enough to fill half a pad. I'm really confused as it what it is?

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