What you describe is completely normal for men. We are not designed for "multiple" orgasms. Some women are, we are not. I would just work on lasting longer with your partner and perhaps other methods, such as oral sex to your partner, for longer satisfaction.
Quit worrying about coming again.... you are putting too much pressure on yourself.
Just enjoy the sensuality and if it happens again, great, if not, so what, you'll have a great time!
Most men I know can not orgasm more then one time. I say as long as you do it right, once is enough.
I think being able to orgasm at least once is a good thing! I've been trying to help people for about a year actually orgasm for the first time!
What I can suggest is during sex, have your partner massage your testicles. It feels weird, but it helps get the "juices" going.
Try different positions and foreplay to help you get in the moode.
Another extreme way is to massage the prostate. This can only be done through the anus.
If you don't want to go THAT far, try the massaging the testicles thing. Also, the area under the head of the penis (most nerve endings) and the area between the testicles and the anus (it can be sensitive and can sometimes cause orgasm).
I hope that helps.