Take Woodie Allens advice, think about baseball.2H2NU05lTGMvRRj6
I knew a guy who had this problem. He made the mistake of asking me about my past sexual life and I made the mistake of telling him. As such he felt he couldn't measure up and soon he was in despair. Every failure makes a guy more convinced of future failures so it becomes a vicious circle.
As a last resort he started taking Viagra - which worked every time. Trouble is - so I'm told - to this day he can't maintain an erection without the crutch of his little blue pill.
A doctor should be your first and most important port of call. There's no quick fix. Therapy - I believe - really works but it takes time.
I may have missed it, but is it just that you cum very quickly? Or is it that you cum quickly and then can't get another erection? They are not the same thing, and don't require close to the same "solutions".
If you can get another erection, I would not worry about it. Just get another erection and have fun. Heck, you can even go to the bathroom and get your first out of the way before you even begin with the gal. That is actually not an uncommon way to handle it.
You may also have performance anxiety to some extent. That can happen if you fixate on what you perceive to be a problem (even if it isn't one).