Ovulation occurs approx 14 days before your period, so there is a risk that you could get pregnant before you even had a period.
A lot of women report problems after coming off the depo shot.
The best/safest advice is to use a barrier method of contraception such as condoms until you get your first period.
But if you are actively trying for a baby then just go ahead and forget about birth control however do be aware it can take some time for your body to return to normal after being on birth control for a long time.