Thanks for all the great replies everyone, good to know I'm not unusual in being this way - goes to show even after a few years there's usually plenty you haven't quite grasped when it comes to sex.
We're normally very satisfied with our foreplay and I always love going down on her before penetration, though she usually doesn't let me take her to orgasm through oral - she says she loves orgasms through penetration more as they are more fulfilling and satisfying to her, so loves oral as a build-up to penetration. As well as this she is somewhat of a one-and-done girl too. She can continue comfortably after orgasm but feels she can't make it to a second one, herself or during sex, so she prefers to make the most of the orgasm. What's fun though is teasing her when she starts telling me to jump on top; defying her and going on with the oral. She gets stuck between deciding to enjoy it or pulling me up as not to come too early. She is an amazing partner in bed though so I'm always looking forward to the main event too of course!
Anyway, I'm only in my first few years of being sexually active so still always trying to improve myself. It's frustrating having the low sex drive which can be disappointing for her when I'm in a low period, though she's very understanding. On my next visit home to the UK I'm getting sleep studies done and hopefully a course of treatment started for the delayed sleep phase syndrome. It throws my sex drive right out the window when my sleeping pattern turns upside down.
Glad to know it's normal not to go through to orgasm before sex, and that I'm not the only one who would take time to recover should it happen. Best wishes to everyone else too!
Avrielle_Aniko, I often read your posts over the forum and find your insight really good to know, it's inspiring that you and your partner have overcome quite some hardship to have what sounds like a wonderful sex life together. All the best for you two.