Help please Is there something I am doing wrong?

Okay I have been having sex with the same guy on and off for the past 5 years, but I have never orgasmed while having sex.! Only when done orally I do but never when we are actually doing it. To me his penis looks big, you know, and I am not loose at all he says I'm tight. When his penis fist goes in it feels so goooood, like I fall back in enormous pleasure and I moan it feels great but then a few minutes into it, nothing.! I don't feel it anymore. I know I get realllllyyyyy wet lol so maybe thats a problem "/ we have tried other positions too they all feel amazing but it never feels like the 1st 5 perfect minutes.!!!!!