Hi,
Obviously I don't know you circumstances and I in no way mean to offend when I say this, but in my experience, I have never been able to orgasm if I am not compleatly comfortable with the person I'm with (one night stand etc). For me, its mostly the mental state rather than the feeling.
Alternatively, I did watch a programme a few years ago (sorry I have no references) where other women were in your situation, (I don't know if they could make themselves orgasm) but they had surgery to inflate their g-spot, presumably making it more accessable. Although it was not properly understood how this would help, the women seemed delighted with the results, even claiming multiple orgasms.
I hope this has been hopeful and I urge you to mention this to your gp, don't worry about being embaraced, chances are they've experinced far worse situations and your health is most important.