Hi, I'm a 23 year old healthy boy. Last week I tried to have sex with my girlfriend for the first time, but it didn't work because my penis was not hard enough to penetrate(totally different to when I masturbate) . I'm not sure if this is an erectile dysfunction, or sth. Actually, it's erects almost every morning, and when I masturbate too. When I kiss her I feel excited, but not hard enough to have sex. After that case I haven't tried to have sex with her again yet. What's this? What should I do?

You should stop masturbating for a while. It is too predictable, therefore your expectations of having actual intercourse are too high.

Too much excitement, excessive masturbation can cause issues since real sex does not have the pressure and speed control nearly the same.

Or it can be nerves, first time or fear, were you using protection, is she on birth control, are you ready to be a father can all cause this

Thanks for yr answer, Chuck!
Actually, I was worried too much at that time; satisfying her because it was the first time for me, and I did't use protection,( obviously, I'm not ready to be a father thought). You have any idea what I should do to avoid such thing next time to get it harder? Another important detail: my balls are not the same size, the left one hangs longer than the right one, and it has some complicated cluster of veins?!

Thank you once again!

OK, thanks for yr answer!