So, I've recently noticed this very annoying problem. When I'm supposed to have sex, my little buddy doesn't want to co-operate. Let me tell you about my current situation:

I'm soon 18. I've been having sex for two years now. I've always had to use condoms, but my new (~1 month) girlfriend is on the pill, so we can go without any rubbers. She's the hottest and most experienced girl i've had so far. She's seriously so hot that i get hard sometimes when i even look at her, and almost always when we kiss (with clothes on).

Everything down there goes fine 'till I'm supposed to stick it in her, that's when my penis goes soft like a freaking pudding. And there is absolutely no way to get it hard again in a while. But if we manage to get it in her before it's too late my thing will function properly. How it usually goes is she gives me some head (this is when I still am hard as hell) and right after that we try to start having "real" sex ("try" because during this time my penis goes asleep). I think it's worth mentioning I have noticed something like this with my previous girls too but it has caused no problems. My mind tends to start wandering around and I can't fully focus on the moment, how can I get rid of that? Now I've also started panicing of will it stay hard or not.

My girlfriend reacts very well in my opinion, if we can't do it she says "let's sleep a while and try again", which always works. She's had more partners and more sex than I have, but this problem down there doesn't seem to bother her as much as it does me. We are not together for sex anyway.

I'm physically okay, I work out and get lots of fresh air everyday, I eat salad and meat and really not much candy or fattyfood or any trashfood. I sometimes have to take anti-histamine for my allergies (cat/dog, my new girl has both), but they aren't supposed to cause anything like this, or at least haven't during those 2 years before. And about porn and masturbation, I used to do that a lot before this girlfriend, but haven't felt the need after I got this hotty

Anyone got any ideas how to improve my performance? :\ I find this really annoying. And I haven't had my testosterone levels checked but I seem pretty normal judging from other things. Oh and viagra and erection rings are out of the question now..