2 years and STILL TRYING!

Me and my husband have been married for two year and after we got married I stopped getting the depo shot. It's been two years now and still nothing:( does it normally take long after the shot to get pregnant? I was on the shot for 6 years and we have already tested his sperm and its normal- and I  have 2 kids already. So I have no clue what could be stopping us from having one! :/