Can’t get an orgasm

So I’ve been having some pretty amazing sex lately, but I still haven’t reached the big O. My partner has been teasing and saying he’s gonna help me get one, but every time I feel I’m about to have one, I overthink it and can’t let myself get there. I’m in my head too much in the moment and prevent myself from having an orgasm, despite how much I’m enjoying myself. Does anyone have any advice on how to counter this? Or any stories of your first orgasm and how you got there?