Q- I live with my dad and he is uncomfortable with me and the lady doctor.

What on earth do I need to do to get him to understand that I'm 18 and need to go to the OBGYN. I have never been and I know I need to go but every time I ask him about it he gets stiff and says stuff like "is there something I need to know about?" Like I'm pregnant. And I'm not. Not even close. Both me and his girlfriend have tried to get him to understand that I have to go because I am a girl. Any pointers on how to get it through to him???