It can take up to a year of the hormones to leave your system. So it’s varies. As previous posters have suggested, OPKs will help you determine when you ovulate and go from there
I had the depo like 3 or 4 times I think and it took me almost 2 years before having a child. I'm not on my second child who's 4 months . One more child and than I'll be okay.