Why is it so hard to get pregnant 😭

Can anyone help? I’m 21 years old and have been trying for 4 months to get pregnant. I started using Pre-Seed last month and I am just so upset that I’m so young and it’s still so hard to get pregnant but everyone around me is accidentally getting pregnant! I lay down all night after sex, I have sex on my most fertile day I do use opk’s, and I’m always on the bottom when he finishes. I don’t know what else to do 😭 I know that there are people out there that try for a whole lot longer than me and I don’t know how they do it because obviously I’m really upset about it not happening within four months. Does anyone have any other tips? Please help!