That's interesting. But you know what...I don't really think it's all that weird or anything. It's all right that you're a "loner." It's actually very healthy to be able to be happy and do things by yourself. Just because you don't live up to others' standards of being extremely sociable, doesn't mean that you're some sort of freak. And not partying is more normal than you think. I have come to realize that not going out and getting trashed every night/weekend is a very positive thing in my life. I'm able to concentrate on actual important things in my life, and spend lots of time with my family, boyfriend, and friends in much healthier and more productive ways. I would MUCH rather sit at home with a book or watch TV eating pizza with a friend than go out to a club or party. I would suggest that, if this is really a burden on you, you begin improving small things every week to maybe make yourself feel a little more "included." Because even though it's fine to be on your own, it still is important to get along with others and fit in -- it's just human nature. After all, in Maslow's Hierarchy of Needs, one need is "Social Needs - Sense of Belonging - Love."
For instance, start by taking part in an extra conversation here and there. You don't need to sit and talk for eternity or share your life story, just give some input - make a comment. It'll become easier and feel more normal to you after time. At first, it'll feel awkward and you might not like it, but you NEED to start with baby steps.
If you're in college, which I'm assuming: Go out of your way to ask someone you don't know in a class a question pertaining to that class. Who knows -- it could lead to some other conversation. If not, at least you'll become more at ease with approaching and conversing with others.
I think one hugely important thing for you could be joining some type of club or group. Search around in your community or college for something you could join. Becoming part of a group with a common interest of yours (politics, reading, science, etc.) is something that could potentially change everything for you. I've had people tell me before that if they hadn't joined a certain group or club they wouldn't have many of the friends they have today, and they'd be an entirely different person.
Good luck and if you need any more help don't hesitate to ask. :)