My SO had this problem back when we were first dating. We treid litterally hundreds of positions. Here are 4 that got her close:
-Modified Misionary: Lie on your back and put your legs over your partner's shoulders. This is a good position if you need clitoral stimulation in order to orgasm, and it is a nice way to begin to experience building a G-spot orgasm. He'll have a lot of control over stimulating your G-spot, and you can play with your clitoris to have an orgasm.
-Mouth and Finger: Ask your partner not to use the tongue as a vibrator on your clit, but to caress your clitoris, urethra and vaginal opening with lips and tongue. Slower is better, so you have time to absorb all the sensations and to remember to relax.
When you feel aroused, ask him to insert a finger, ever so slowly, and rub your G-spot very slowly but firmly. Over time, your G-spot will become more easily aroused, and swollen, and less stimulation will be necessary to feel ready for orgasm.
The point of this exercise is to relax and allow the sensitivity and pleasure to grow and evolve by shifting your focus bit by bit from clitoris to G-spot, over many lovemaking session.
Face to Face on a Stool: A tall kitchen stool is perfect for communicating and slowly working up to soulful eye-to-eye communication. If you are used to closing your eyes and burying your head in the pillow, you'll find that in this position you are more present and equal. No one's weight is on anyone, you are facing each other (he's standing and you're sitting). You can look down at his penis, and he can get valuable feedback about the types of strokes he is delivering when he sees your face and hears your delighted sounds.
Because this position provides intense stimulation to the G-spot and a clear, direct way to communicate, this is the best position for both of you to learn how to awaken and stimulate your G-spot. Your clitoris can also be easily stimulated.
This position is excellent for deep penetration -- if the stool is sturdy -- and for exploring how deep, penetrating thrusts can trigger the sensations of a uterine orgasm (different than a vaginal orgasm, but equally enjoyable). It's likely that at first you may not have an orgasm and you may not ejaculate, but it's worth it to explore a uterine orgasm.
Stad from Behind: This position borrows certain elements of the popular "doggy-style" position, where the woman is on her hands and knees and is entered from behind. But if you try standing up, slightly bent forward, you'll find more pressure on the G-spot than with the traditional doggy-style position. Your partner's movements will push forward against your G-spot, and that's exactly what you want for good stimulation.
In all these sexual positions, it is important to have your G-spot aroused before he enters. Expressing your delight in your growing sensitivity and arousal is the best way to communicate with him. If he hears, "Oh, oh, my gosh! Oh, that is so sensitive!" he will slow down, but stay aroused and excited. If you say, "I need you to slow down," especially in a nonerotic voice, he may feel he is being dictated to or worry that he is not pleasing you. His fun and confidence will be affected and he may lose his erection. G-spot sensitivity, G-spot orgasms and ejaculating freely will not happen overnight. He'll learn a few things, and you'll give up a few things while you wait for him to catch up. Let him know when he really hits the target. It's helpful to say to your partner, "Oh, oh, oh, please remember that spot!" That gets the message across in an exciting way.
Don't expect him always to remember, but do expect him to catch on after a while. The great thing about all these positions -- and more generally about learning to awaken your G-spot -- is the gradualness with which this can occur. Unlike learning to have an orgasm, which often leads people to stick to one method, variety in how you experience pleasure and orgasm will increase as you slowly incorporate your G-spot awakening into what you already do.
One thing you might consider is the Slightest Touch machine (
http://www.slightesttouch.com/). This machine has been able to allow my now wife to reach more orgasms in less time with much greater intensity. *warning* do not go full power the first time.