Ok, I googled Depo Provera for you, and it says:
"Women who want to become pregnant may stop using Depo Provera at any time. For some women fertility returns immediately. For others it may take 6-18months or longer for the body's hormone cycle to return to normal".
Sorry if that's not what you wanted to hear, but realistically it could be any time for you as everyone's different.
My friend took 3 years to conceive after stopping her contraceptive injection, and had even started the ball rolling for fertility treatment but then fell naturally anyway.
Good luck, hope it works itself out! ***