Wanting baby #2

I've been on depo since August 2014. I've had 3 shots. My husband and I are wanting to have another baby. I was suppose to go back and get another one on August 5th-15th, but I didn't. I was never on birth control until last year. How long does it usually take to get pregnant? And to get out of your system?  We've been trying ever since I was suppose to go back.