Help please TTC #1

Been TTC for #1 ... 4 months now , doctors say I'm perfectly healthy but then how come I'm not pregnant yet? I'm so tired of missing periods and my body playing jokes on me each time I go to test . I just want my miracle baby here. My boyfriend has two kids from another lady and he said it took 3 year till she conceived baby number one and conceived baby number 2 faster than baby number one I'm not sure if she had something wrong with her or maybe if he has something wrong with him and he just doesn't want to get checked out because he's scared I'm scared too so what if its not me that's the reason but we aren't conceiving we will never know and he just doesn't understand I'm so hurt and so lost baby dust to you all