What Causes Lack Of Period After Stopping Depo Shots?

My last depo shot was in June 2010. I still have not had a period. I have no idea where I should be in my cycle because I have not had a period for 2 years!! I'm concerned about infertility as my husband and I are trying to conceive now. How long will it take for this medicine to leave my system and for things to regulate again?