Two-thirds of all women cannot have an orgasm from vaginal stimulation. You're perfectly normal in that.

Do you masturbate? Masturbation is the way we learn how our bodies respond to certain touches, and we can teach that to our lovers. Also, telling your boyfriend how you like to be touched, and when he's touching you right, will help him learn what stimulates you. You should also tell him what doesn't work for you, in a nice way.

Some women don't come very fast, some do. Both of you need some patience and relaxation, and don't worry if it hasn't happened in a short time.

One position that might help is for him to enter you from behind, while stimulating your clitoris with his hand in front.

A very important thing is to have enough foreplay before he enters you. If he can get you really aroused first, you might find it easier to come, whether vaginally or clitorally. Have you tried sex toys and vibrators? They might help, and they can be fun for both of you!

Unfortunately, guys have big egos and sometimes put too much pressure on their ladies to have orgasms, which only makes it less likely that she will. There are many books that might help him understand it's not his fault OR your fault if you can't come from intercourse. Here's a highly recommended book you might get:

She Comes First: The Thinking Man's Guide to Pleasuring a Woman