Hi, and thanks for your query on eHealth forum!
Actually, it is very difficult to predict whether you have post depot shot amenorrhea or absence of periods, or if you are pregnant. Ovulation returns anytime about 1-6 months after stopping the shot. Also though appearance of periods is not related to ovulation, this too may appear any time within 6 months after stopping the shot.
Hence to avoid confusion, it is best to consult your gynecologist and test for pregnancy now, and about two weeks later. If this is negative, then go for an alternative method of contraception. Use barrier contraceptives until you start something else. Please discuss with your gynecologist. Hope this helps. Take care!