Basically, I'm an absolute idiot. I've just been on holiday, and on a very drunken night I allowed a girl I was getting close to during the whole holiday to convince me to have unprotected sex, being in a very drunken state I allowed this to happen. She said she's on the pill and has been checked, and being in the condition I was, this was good enough.
There was only very brief penetration, but my main concern is that for a few days after my penis was very very itchy, and it only died down about 4 or 5 days after the incident. Do I need to see someone?
You can't get a diagnosis over the internet so no one here can tell you if you're ok.
Only a doctor and some tests could determine that.
It is possible though that you might have just gotten a yeast infection, but that doesn't mean you don't want to rule everything else out. If it is an STD it could be treatable, and best done early. Also, it's irresponsible to continue spreading it just because you don't want to go find out if you have one.