Depo unfortunately takes a while to get out of your system and for you to ovulate normally...up to 18 months or more for some. It's a frustrating process, but in the meantime, you could talk to your doctor about your concerns. You can also invest in ovulation predictor tests to help you know when you do ovulate and increase your chances of conceiving.
Good luck!
Unfortunately theres isn't much you can do. Depo stays in your system for up to 2 years. It could take up to 18 months after your last shot to be able to conceive. I was on depo for 3 years i took my last shot March 2013 didn't get my period till December 2013 and i am now starting to ovulate again.