How long does it take?

Ive been on the depo for 9 months now and I missed my last shot on may 10th. But me and my boyfriend want to have a baby now. Does anyone know how long it would take for the depo to get out of my system? I have been bleeding and spoting lately but im pretty sure thats normal. I read that since i only got 3 shots that it should only take a month? But i dont know.