This is actually a pretty common problem that guys can have when they loose their virginity. There are a couple reasons that you could not be orgasming. One reason is that you just aren't accustomed to sex yet and so you haven't really learned the ropes of getting yourself to orgasm this way, while you've most likely had years of practice masturbating and learned exactly how to get yourself off this way.
Another possibility is that you were just stressed out and worrying about it being good for her, so you weren't able to relax and experience pleasure. Once you start thinknig about that, then you'll start worrying, "Oh my god, there's something wrong with me, this is probably awful for her...." and that will just stress you out more. It's pretty difficult to reach orgasm if you aren't relaxed.
There is also the possibility that you take a while to orgasm via sex. Some men are done in a minute or less, some last around 5 to ten minutes, some last a half hour, some can go for an hour or two. Just because you weren't there in a half hour doesn't necessarily mean that there is anything wrong with you or that you are doing anything wrong.
Then, as openminded suggested, there are things like drinking alcohol that can delay orgasm or make it impossible to reach orgasm.
So... don't worry. You'll get the hang of sex after a while and you will be able to orgasm.
