2 week bleeding before shot

It's almost time again for that 3 month depo shot. I start cramping early today and though it was lack of sleep but at 5pm I felt a warm sensation that I though was cum since I pleasure myself two day prior and was horny earlier also. Does anyone experience bleeding two week before getting the depo shot again? I won't have a period for the whole time on the depo expect the one week before i take another shot.