Nobody can tell you. If you weren't on any birth control at all, we still wouldn't be able to tell you. The average healthy couple can take up to a year to conceive. You could get lucky and get pregnant your very first month of trying, or it could take a while. It's all a matter of timing - you have sex around your fertile time, the sperm has to meet the egg, travel down, implant in your uterus before it's reabsorbed by your body, and then it has to hang in there. Some women miscarry before they even know they were ever pregnant. Sometimes the hormones don't build quickly enough to stop your period, and the egg is flushed out with your blood and tissue.
So you see, it's not as easy as telling you when it will happen. You'll just have to be patient, wait for the depo to leave your body, and then try. Good luck.