Please be prepared for a lengthy analysis of my issue.

With that being said... I'm 18 years old, I recently lost my virginity with a girl that I met at a party (we didn't have sex at the party, it was about a month later when we met up). She called me and said she wanted to meet up with me at my apartment for our first date (up until now I was still a virgin) so we watched a movie, spooned, etc. and finally we started taking eachother's clothes off at which point she asked me if I was a virgin and I told her yes and I told her I was ready to do this. Keep in mind this is only the 2nd time I've met her, and things are already getting hot and heavy, but I can tell she likes me a lot.
So we get ready to do it and I have an erection the whole time until it's time to put on the condom my erection starts going soft and I can't keep it up... with a little assistance from her I get it back up, put the condom on... and it goes limp again... so she gets it back up again and I finally penetrate her. After about 5 - 10 minutes of penetration I'm still not able to cum and she says she has to go home, so we call it a day.

The next day she comes over again and we decide to try again. During the whole time she's here I have an erection, until she starts unzipping my pants, at which point I start going limp again... she gets it back up after a few minutes of trying and I put the condom on, after I put it on I go limp again and am forced to take it off, then she gets me hard again and I put on another condom and I go limp AGAIN! So now she asks me if I'd prefer her to give me head and I tell her yes and she starts giving me a blowjob / handjob. This is where it gets interesting. During the blowjob my entire upper body goes completely numb. After a few minutes I start to get ready to cum and then she switches to giving me a handjob and all the built up momentum to cum is lost and its like starting over... so she continues to stroke me and again I get close to cumming... then she switches to giving me head and it starts over again. Finally, after about 10 minutes, my penis decides to go soft and she says she has to go home or she'll get in trouble, so, again, I can't climax.

Does anyone know what the problem could be? I'm pretty sure its not the attractiveness of the girl that's stopping me from climaxing because after we're done I masturbate to us having intercourse. I'm thinking its probably because during intercourse I have so many thoughts racing through my head and its very hard for me to concentrate, plus this all happened so fast and I haven't really built up any feelings for the girl since I hardly know her combined with the fact that I'm absolutely terrified of getting a girl pregnant. I'm pretty sure the girl isn't sleezy because she says I'm only her 3rd, and we share a lot of the same friends and none of them have anything bad to say about her. The girl told me that maybe we should take it slow and get to know eachother more before we have intercourse again, and I gotta admit, I agree completely.

If anybody has some advice for me or knows what the problem could be, I'd greatly appreciate it.

Thanks for your time