Birth control "shot" and becoming pregnant

I have a huge question and hope someone can have an answer , i had the shot a few years ago before and in between my two pregnancies, i became pregnant right after missing a dose or stopping 5years ago, i recently started dating and have had unprotected sex many times and didn't get pregnant , i took nothing after Hoping i would get pregnant. I decided to get back on the shot "for period purposes" , would it be harder for me to become pregnant since it already has been a problem once i stop it ? I'm 25yrs old and want to get pregnant again before im 30yrs old