Hahah, so I come to this thread to find that my name's already been thrown around, oh why?
Anyways, I think a lot of things that I've wanted to say have already been said, but there are a couple of things that I want to add.
Firstly, relationships and education are two completely separate things. Just having a girlfriend doesn't mean that your VCE will be affected and just because you're single doesn't mean you'll do any better. In my opinion anyway, you have to do what makes you feel comfortable and happy. Look at it this way, if you're in a relationship that makes you happy, you'll find that your life through year 12 is much better, just because you are happy.
Secondly, I think what you need to do (to the OP), is to just stop looking for a relationship. Those things come, what I mean is that, you never know when you meet the right girl. Don't do what I did for a period of time and go out there to meet and get to know girls just for the purpose of finding a girlfriend - it never works because you either get friendzoned, rejected or your relationship will be short term because it's not built upon a solid foundation. You have to really just chill and be open - that's the main thing - just remember it could be any girl.
Thirdly, the best thing you can do, in my opinion, is to just make yourself more attractive!! So that's the little things, get a nice haircut, shave, wear nice clothes and just all round try to actually look nice everyday, not only will it help with girls but it'll also help you feel more confident and confidence is a big factor if you're looking for a relationship. Then after that you can start to improve other things such as going to the gym, getting to know friends who will be able to introduce you to more girls...etc. Then you can look to changing your personality as well - of course, be a nice guy, but don't be too much of a nice guy, you have to have something that the girl you like will want, and she has to chase it, I don't know, just don't be clingy and don't be like her brother

I still think the predominant factor, however, is to not get caught up in finding a girlfriend, just let go and let the good things come to you. Everyone will find a girlfriend some day, even guys that you wouldn't expect to have girlfriends all will in some time. Just let it be and you will find happiness.
Btw, what I've said applies to finding long term relationships. If you're like some other kids I know and you want pretty much short term girlfriends (date for a couple of months, break up, get with someone else, repeat...etc.) - then you're just going to have to get to know as many as possible