If it's not an orgasm, what is it?

So whenever my boyfriend and I have sex I'll feel like I do have an orgasm. Almost every time. But I just read that it's rare for women to have vaginal orgasms. I don't try to lie and say I've had one and faked it, I really do feel like it happens every time. But if a vaginal orgasm is rare then why do I feel like I end up having one? I shake and I mean it doesn't match up to the orgasms I get when he eats me out but it still feels amazing. What could be happening if it isn't an orgasm but feels like one? (Also after it happens its always like a freaking ocean down there so that's another reason I always thought it was an orgasm.)