I don't know if its a problem...
Or I lack concentration, or anything else.
But the past 4 times I've had sex, I couldn't come, the last 2 have been with my newest girlfriend. She lost her virginity with me and we did it for like 30 mins but we stopped cause it was hurting her, but the next day we went at it for almost 2 hours, and there were times like I could feel I would come, but I wouldn't get there, even she asked "You haven't finished yet, right?" ... I told her, at about 1 hour 30 mins that we should get going cause my parents were going to arrive (as we were leaving my dad came lol) ... But even then, she told me to take off the condom to feel more, and without the condom I indeed felt more, it was more pleassurable, but still, no coming.
And its driving me nuts, I don't want to do it again with her, maybe it will be the same ...
Has anyone ever experienced this "problem"?

Maybe you should cut down on your solo-play, keep more juice in the bottle

This is not a "problem". A lot of guys experience that they can't come during their first few times - or even more! This is all psychological (could be biological as well, but the chances for that are less). You could feel a certain nervousness over having sex and cumming. When you start feeling insecure during intercourse, usually you will have "cumming problems". Remember to just relax and go with the flow. Don't THINK TOO MUCH during sex. Just fucking do it. Just fucking fuck.

I've had similar problems. A lot of guys have.

First, get it out in the open with your girlfriend, address it once. Tell her you are thinking to much. Tell her that you are a little pretentious about sex and are not quite able to relax completely (yet.)

If you have been this intimate with her already, she should accept it just fine and be understanding, particularly if she's as inexperienced as you say.

That should take some of the weight off of your shoulders. You should not have to talk about it again since you've addressed it and come to an understanding.

Then just stop thinking so much. Or, in my case, think about specific aspects of the sex as it's happening.. like what's happening right now. Not the future, or the past.. the sensations, parts of each others bodies etc.. Just enjoy being naked with her. Don't think about finishing. It will happen on it's own.

Don't psych yourself out. If you worry that you're not going to... you won't. Know that you will. Envision it, envision her reaction to it. Stop trying to control it, just relax your muscles and know that it will happen when you're ready. Also, it might help if you let her do all the work.

Most of all, just enjoy the experience. Even if you don't finish, you're getting down with a gorgeous chick right now. How awesome is that?

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Live Your Truth.

Most guys want to last longer so try to look at this in a positive light...most women wont complain that you last to long lol only that you dont last long enouph.

Now what should you do? Try to just relax and enjoy the ride, allow your self to get turned on and rather then thinking "sex is only over when I cum" think "The whole event is fun and Im just gunna go with it". Also try some forplay with the girl to get you both really turned on!

Hope I could help but If you still cant then mabey see a doctor?

Maybe you're just not doing it hard/fast enough.

If I masturbate, i can come pretty fast because i can apply the right pressure and speed n stuff.

When I'm having sex I also have 'trouble' cumming, but a position like doggystyle or cowgirl does the trick for me, because I can thrust really fast like that and that helps me cum a lot quicker. If i'm doing it missionary or similar things I just cant thrust hard enough, maybe that helps you too.

Oh yeah and also, try to stop masturbating for a couple of days and then see how it goes!

Keep a warm batch in a plastic container that you could throw on her when she's not looking? Nah just kidding. Keep at it, practice makes perfect