If you want to get off with someone else, you usually need to have the ability to get off relatively easily on your own. Not to get explicit, but is the one position you're able to have an orgasm lying on your stomach? I ask because a minority of women masturbate this way, and they're usually the ones who have the hardest time orgasming any other way.

(Of course psychological factors and/or meds can be a huge part of the problem. But that may not be the only thing.)