Ive always had the g-spot orgasm. The first time, I thought I peed all over him.
My spot for this is found when I'm on top riding back and forth. Works every time after I tell him to be still.
Sounds like your body may be climaxing....but perhaps you mind isnt allowing the full affect. For me it requires total freedom of the mind, total relaxation of the mind. If I think about it, I try too hard for it to happen and then it won't. And also, if he's unhappy that you're not "getting off" that's just adding to your mental pressure. Need to talk with him, tell him you're learning about your body and what it takes, and you need him to be patient. Otherwise you'll turn erotic pleasure into functional "I NEED to have an orgasm!".
Relax......perhaps try meditating to learn how to totally free your mind.