what am I doing wrong

I never thought ttc was going to be so hard for me. Everyone in my family has no fertility issues, every single person in my family had sex and bam! Baby. I wish this was my case. Idk what’s wrong with me why is it so hard? My period is extremely accurate comes same day(1/2 day after/before) every month regular flow every-time. Doctor says I’m perfectly healthy. my boyfriend perfectly fine. what other reasons can prevent me from conceiving? I’m in my early 20’s & i just don’t know, not one pregnancy ever, never been on birth control. How come it’s so easy for some and so hard for some? Maybe I’m doing something wrong?