I know exactly how you feel man, did you see my previous post? Same problem. I did some research and the most common reasons for this (that effect guys our age) are emotional and drug related. Are you on any kind of blood-pressure affecting medication? Or antidepressants? These can affect performance.
Also, say your girl is really, really hard to please and you lose your erection once...You'll get anxious next time and lose it again because you're so worried about it you can't focus on her or the sex, only worrying. If this is the case, thy not to think about it at all. Don't be thinking "come on...Get hard...Get hard..." but instead focus on how her lips feel on yours, or how her skin feels under your fingers...Etc...Etc and it will help.
I was both having sex and looking at porn sites daily, and I think the constant sexual surroundings "numbed" me to sexual situations, so things didn't turn me on like they used to and I couldn't perform. I've taken only two days off from porn and already feel more aroused around my g/f and in said situations. Maybe too much stimulation, if you look at porn a lot?
Good luck!

Thanks bro.
I am doing the same thing with the porno break actually and it seems to be working. I haven't watched porno or rubbed one out in a few days and tommorow I am looken to get her to do it haha. Thanks

Are you on any medication? Or drugs? It could be ruining it. Or any recent trauma's?

~jennifer~

Hey try and not have sex or anything sexual for a week or so and see if that helps. But other than that I dunno!! Sorry

alison xoxo

Not looking at porn period would be good. I know it sounds typical for a girl to say... But i'm serious. Porn tends to lower your view of normal girls in general without you even noticing and then when you stop completely and you start just looking at your girl it'll be like "wow" hard on city... It worked w/ my man :d