I had sex for the first time with my girlfriend. I love her and she loves me. We have tried having sex before this but I had problems getting and keeping an erection. We had concluded that this was because we had too much foreplay. So on this occasion we still included foreplay but substantially shortened it. During penetration it felt good but I never felt close to an orgasm... inevitably I had to fake... I am 17 and haven't the slightest idea why I wouldn't find sex pleasurable...

Well maybe because you need to relax.

First time, second time, third time and whatever it might be. It takes time, takes practice and no one really works miracles.

Just be open and honest and experiment.

As far as having orgasms, it is not necessarily the most important part of a sexual relationship with somebody.

Orgasms are not what sex is about.

Sex is a uncomfortable thing for people who it doesn't come natural too, and some people are not natually sexual people, or enjoy sex at all.

Sex is about being completely open and committed to someone, because it represents a bond with someone that can't be broken.

Unless your in it just for the pleasure, then it's a vice.

I had sex for the first time with my girlfriend

There's your answer, it's your first time !
It'll be great on the third go.. .

Sex for the first time is uncomfortable with anyone unless you are both highly experienced,
Have no inhibitions and both know what you want.

You need to be into the enjoyment of the moment and not in inside your head with.. .
"am i doing it right ??".
Sex will become as natural as breathing once you've completed your learners license.