Fourplay, fourplay, and more fourplay.
I would guess that 5 minutes is pretty normal for a sex-newbie. At 4 minutes, 30 seconds you can take her over to the dresser, change positions, and get back to it. A little brake like that may well reset you 5 minute timer back to zero. If it works the worst that will happen is she wonders why you lead her all over the house during sex. If you two are monogymous and have both been tested, then oral sex is your friend. Go from oral to penetration, when when you are close to poping your cork switch back to using your mouth on her. Oddly enough very few women will complain that you have stopped humping under these conditions. You can switch back and forth and go a looong time. Oh, did I mention fourplay, fourplay, and more fourplay?
Two quick thoughts if you are new to sex:
Lasting five minutes is more than enought time for you to be able to experiment and try out different things. That and a desire to learn and improve pretty much means you can train your self to last as long as you want.
Oral sex: get good at it.