All right. I think I might be able to relate. A little, anyway.
When I first started getting down to business in
college, I would have to literally psyche myself IN to be able to get off with a girl. Even when they were actually pretty attractive, and I would be thinking, "I KNOW this chick is hot, I should NOT have to be thinking about something else to get off", but I would. And then I would think, "well, why should I even be thinking like that in the first place??" - which would compound the problem. I would spend most of the time thinking about thinking, and less time about how good things felt.
PLUS, you compound that into a healthy self doubt from carrying a few extra pounds (I used to be a fatass in
college), and a pretty much 'average' sized wanger, and you have a real problem on your hands - so I definitely know where you're coming from.
A couple caveats: #1. By packing 'average' I mean I'm just under 6, not 8-9" like apparently everyone else around here. And nowadays, I'm totally cool with it.
#2. Sometimes the girls are just butt ugly, and you sober up during the act, and realize that you're just never going to finish. This would be a good time to cut your losses, smoke a bowl, and listen to some music (maybe even with her...!) [If you're her ride home....]
But the good news? There is salvation, mate. And it's all within you. I would wager that your problem is 95% in your head - unless there is some weird thing happening with the plumbing/nerve endings downstairs, but I doubt that.
If you are fat, then I recommend losing weight. It was MY self image that was a problem for me during sex - never mind that the girls thought I was good-looking enough to lay down with - I KNEW that I wasn't good enough, and that they must have been stupid for even bothering with me. But once I started shaping up, caring a bit more about what felt good for ME (I was also pretty much just in it to please her), and took more of a devil-may-care attitude, then things went much better. For both of us. Don't neglect her needs totally, mind you, but bear in mind that her 'needs' might involve a lover who isn't such a
pussy.
It may take a girl you really care about, and who loves you no matter what you do in bed to really get to you (I didn't care about a lot of those girls) - and break you out of your shell....or, it may come in time (heh). But I think the goal for dudes that have this problem is to try to get to a place (mentally) where you feel like Patrick Bateman in American Psycho.
When he's banging the hookers, checking out his guns in the mirror, and generally having the time of his life. Believe me, he is NOT second-guessing himself in that scene.
Hope that helps.