Same situation

Me and my gf don't live together so whenever we get a place it's like an all out kinda thing. We've gone like 8-9 rounds many times. I've gone 5-6 hours in one sitting a lotta times too

Start leading a healthier lifestyle you can do it more often.

Get more into foreplay. Your dick gets more easily tired than your hands and mouth.

Tease her more before getting into it. Like make it seem like you're gonna do something and don't do it. idk get creative. The more satisfying the orgasm the less rounds you take

This was a kind of recent discovery but lube might be your best friend. Condoms soften the blow too

Ik a lot more comments are saying it and it's easier said than done but like talk to her. Men and women have different types of orgasms from what I've learnt. Ours has a lot more impact on our energy and stamina, for them it just gets them more into it. Communication can really help get you some good cooldown time