My female Sim wont become pregnant

My female sim won't get pregnant no matter what I do

I have recently just got back into Sims 4, I deleted both the game saves I had because I wanted to start fresh and I made a family, two young adults who are married and one child (one of the young adults siblings) I dont have any pets nor any other household members. Just my two young adult sims and a child, both young adults are quite a while away from ageing up. I have the "try for baby" option, but every time I try - my female sim doesn't become pregnant, I wait for a few days and nothing happens. I dont use CC or mods so I dont know what's going on.

Is it just a case of trying and trying until it happens or do I wait it out and cross my fingers in hopes that it happens

Any help given is very much appreciated