Girls, how do you protect yourselves? They say on the GYN it's hard to…

Girls, how do you protect yourselves? They say on the GYN it's hard to get pregnant. How true is that? We're on combined contraception. I don't want to risk it) and can you put a coil after the first child? I heard that you can't put one after the first because then it will be difficult to get pregnant. In general, my head is spinning ? I don't know who to believe. I plan to have a baby in three years.