Stipe
I used to have a similar problem until I read about a breathing technique in a Tantric sex book. It worked immediately for me. All you have to do is to concentrate on breathing in and out slowly. It's almost like meditating except that you can also be involved in what you're doing. Think about the breathing as soon as you penetrate. If your mind wanders, the rising sap is enough to put you back on track: think breathing again.
It gave me an enormous amount of confidence to find something that worked so consistently.
My partner at the time I first tried it was very multi-orgasmic at the best of times but I had to use tongue and/or fingers once I'd shot my load. The first time breathing, she had several while I was inside her. Admittedly in fairly rapid sucession. She was over the moon, so was I.
Another thing to try is a cock ring, although I prefer to tie the base of my erect tool with kitchen twine. That really did extend my time to an hour or so and enabled me to thrust as hard as my partner wanted. We quickly discovered that if I restarted thrusting as soon as her orgasm died down, the next followed rapidly. Achieve that a couple of times and you'll believe you're invincible. The added benefit is that the twine increases the cock's girth and hardness. If she likes it in the arse, it's just the most perfect solution.
Neither technique has ever failed me since (when I get the chance to use it, that is). But I prefer the twine. It usually means that my partner is more into what we're doing because she has to know that there's a purpose to it all!
Talk to your partner. She's the best helper you'll ever get. She can remind you to breathe and she can also tie the twine!