No Orgasm Nelly

I literally don't know what's wrong with me. I'm just going to be blunt, my SO is hung like a horse and definitely knows what he's doing... But I still can't get off. I am a terrible overthinker and I think that could be part of it. Instead of just relaxing I'm tense and my mind is always going about 90 miles per hour while having sex. lol it's terrible. And I always feel like I'm so close but it never happens. Anyone else have this problem??