how can i reach an orgasm?

i don't know why but it's very hard for me to orgasm vaginally. through oral, easy, but my boyfriend always gets self conscious about not being able to "get me there". he's amazing in bed and i tell him a million times it's not him it's me.. are some women just not able to do it? or do you have to learn how? im very confused on why i can't do this either, what could be the problem?