Well, hello there, Nemo!
I can tell you something: Everyone's body is different. While some women can have mutiple, powerful orgasms in a short time, other's can't. As guys have big penises, others don't. As some women have big boobs, other women has small ones, Some people dislike oral, other dislike anal, and I can keep going for a looong time.... Bottom line is: Maybe you are a little harder to get to orgasm. There are several books to show techniques on how to orgasm for the ladies, go do a quick search on Amazon, and do a little research on them before buying it too. I would reccomend some, but sadly I can't recall the name of a book a friend of mine read. I'll look for it too.
However, learning how your body acts and techniques to change that is good. Maybe some positions or other sexual stuff makes your orgasm to come faster, or better, or longer, or all of the above!
Oh, and talk with your man too. He might be a little disappointed that he is not able to set you off, so let you know it is not about him, but about you, and that you need his help to figure this out. Talk, talk, talk!!!
I wish you good luck, and a happier sex life too!
-Jean.