How to get pregnant on the dep shot?

My boyfriend and I want to have a baby. I have been taking the depo shot for the last 6 six months. This is my 3rd shot. I am suppose to go back in June to get my 4th shot but i am not going to get it. We have been trying to have a baby for the last month since before i got my third shot. Is there anyway i can get pregnant before i quit taking the shot? Also i just got my 3rd shot like 3 maybe 4 weeks ago and i am spotting already. Usually i dont spot until 3 weeks before its time to get my next shot what could this mean? How long does will it take after i stop the shot in june to get pregnant?