Personal Trainer with erection problem

So I've had this problem since the first time I had sex. The first time was a fail, so I tried the next day with her to get it up. I did get it up but I'd say only about 70% up. I was embarrassed. Well, now two years later I am 20 years old, I work out regularly in the gym, I run and mountain bike (haven't been outside for couple weeks). With me being in shape and being young I find it hard to have "ED". I think it's more of Anxiety.

Although, I have a bit of experience so I'm not nervous. I know exactly what to do to get a girl turned on and I know what she wants. I am confident enough to not be nervous when I'm fooling around when she's on top but once I get ready to put it in and I get on top, it feels like the blood just drains out of my penis and it slowly goes down and I think "wow.. not this again.."

I don't drink but once a week, no smoking or drugs, hardly any fast food, plenty of fruits and vegetables, exercise 3-5 times a week, and low body fat %. I'd like to know a little more about why this is happening to me because yes, as everyone has said, it is EXTREMELY humiliating. My girl is understanding but, i still feel incompetent.

Thanks

[palpateit]

Have you used Interent porn consistently over an extended period?

Not sure if this is the problem, but it is the cause of most ED issues for men your age - the use of internet porn. We have seen so many men with this problem, and the "experts" don't have a clue. They don't understand neurobiology of erections, or how Internet porn can alter the brain. So, it's porn, not masturbation that can do this to men.

Start by educating yourself.

Here's the thread you should look at for porn-induced ED. If you control find - "palpateit", you will see my posts. The first 2 posts have links to presentations and articles about porn-induced ED.
http://www.medhelp.org/posts/Mens-Health/22-with-porn-induced-erectile-dysfunction/show/469209

[jr_inmex]

If fooling around while she's on top gets you aroused, then try having sex with her on top.  It doesn't sound like you're interrupting things to put on a condom (an activity which by itself can kill an erection if it takes too long), so try the girl on top position.  I think you need a success, after that things should improve given your age and excellent fitness.  It's anxiety - you might even try a small amount of alcohol to relax you beforehand.  

[buttosn]

Thank you for the input. I will avoid all porn and videos from the internet from now on (at least until this changes). However, I don't consider "porn" to be what I watch. I'd consider it soft-porn. I differ slightly that, I can actually not stimulate myself and achieve erection, almost full, all by itself. I've tried it when I was a kid, and I still can. Just look at it and it goes up. I don't know? But I figured if I can do that, then if I have a girl that should be easier. I think maybe it has to do with masturbation but I've tried not masturbating for 3-5 days before any sexual behavior with her. Nothing has worked so far, but I will give two weeks (from now till next weekend).