I wish I wasn’t on my phone and I could insert an image easier, because it’s important you both know where a G Spot is. Google the phrase “O Spot Diagram” and you will see an image called “Figure 5: Deep Erogenous Zones…”. It’s a shitty diagram but if you look close enough it shows you the G, A, and O Spot locations, for the average woman.
The G Spot is not really hard to find; it is easily the largest zone inside you that can make you cum. The diagram above underestimates it in my opinion. My guess is, he is going right past it. If you are on your back, laying flat, and his palm is facing towards the ceiling, once he is to his second knuckle, if he hurls his hand up, his fingertips are right on your G. All he needs to do is motion “come here” over and over and over, at different pressures and speed, and you will be in heaven. Eventually, enough of this and you will experience a different kind of orgasm; from the reports I’ve had, it’s a full-body, less-intense, linger-lasting feeling than a clitoral orgasm. God I envy you ladies for getting different orgasms.
If he shoves his hand deeper, he will eventually hit your A Spot, but it is way smaller, and I suspect that is what you are having hit sometimes, and the only way to really consistently keep it going is with something bigger than a fingertip, like the head of a dick or a toy.
The problem is: women need to be worked up to that zone being fully ripe for orgasm, so fingering it, intermittently and inconsistently, will give you exactly what you are experiencing: “oh that feels good. Wait, where’d it go? Do that again? Please. What happened?.”
Now the real mind fuck is this: a dick hitting your A spot, a toy in your ass pressing your O spot from the back, his fingers wedged inside you playing with your G Spot, and yep, a free hand to tend to your clitoris. Now you can begin to see what life looks like in my bed. A total cataclysmic mind fuck. Add some eye contact in there and you are done for. I get to get up, stand upright, and witness the havoc created in a face down, can’t-move woman. It’s so fulfilling.
Stay with it. It sound like you have a good guy who wants to discover your body with you and make sex amazing. Soon enough, you will have the 4 point stance; and you will lose your fucking mind. You will be the girl face down, can’t move, and your man will feel like the world was built for him.
Revised. Added diagram. (Thank you FapBook Pro).