Why is it harder to conceive baby #2

Stephanie • 23yrs old. Have a 2yr old baby boy. Trying to conceive baby #2.
When I was 18 and 19 years old my boyfriend and I never thought about having a baby he would always pull out So that I wouldn't get pregnant. But we found out I was pregnant twice and ended up having 2 abortions. When I turned 20  I found out I was pregnant again so this time we kept it. But the thing with these 3 pregnancy we NEVER tired to have a baby it just happened even when he pulls out.  And now we are blessed with a 2 years old boy. Now that he's 2 were now trying to conceive baby #2 for the past 2 months. So for the past 2 months we've been trying my period has been coming late making me think I was pregnant. So my question is why was it easier before when he pulled out verse now when he doesn't???