Unfortunately, my general observation is that most of us don't really change our core personality traits, level of confidence included, unless we go through something seriously terrible. I kind of understand where you're coming from, I've never been the most confident person in the world myself, and while I have occassionally stood up for myself, for the most part I'm kind of a quiet pushover who sits in the corner waiting for someone to tell him what to do. Still, I don't think it's impossible for you to either change or find a niche into which you fit perfectly as you are.
I don't know if you're familiar with cognitive restructuring at all, but it's something that might help you if you want to try and become more confident. The basic idea of cognitive restructuring therapy is easy, and it's something that anyone can do. Therapists who use cognitive restructuring believe that the roots of our negative emotions (fear would be the case in a lack of confidence) is in the faulty assumptions that we make. That is that we assume that an event causes an emotion, when in actuality an event causes us to make an assumption on a pre-conscious level, which then causes the emotion. How cognitive restructuring works is to have us analyze our thoughts about an event, finding the faulty assumption, and correcting it. As time goes on, the process becomes natural, and it can lead to a change like more confidence.
An example of cognitive restructuring would look like this.
Event: I tripped and fell in the middle of the cafeteria
Feeling: I feel really embarassed
Assumption: People must have seen me trip and fall, now they think I'm stupid, clumsy, etc...
Now that the assumption has been identified we go back and ask is it a reasonable assumption? The truth is that it really isn't. We've all tripped before, anyone who acts like they haven't is just a douchebag trying to look cool. Not only that, but to assume that everyone saw us trip is also probably false. One near universal faucet of human psychology, is that we generally assume that more people are paying attention to us than actually are. Even if a few people saw my hypothetical trip, most of them didn't, and those that did probably didn't care.
This structure could be used to address confidence issues as well
Event: I want to talk to that girl
Feeling: I feel too nervous to talk to that girl
Assumption: That girl probably doesn't think that I'm cool, she'll turn me down and it'll be really embarassing.
Again, we analyze the asumption, and while it could be true, it's probably not. If the girl has never met you before (and if you're going to college there are going to be a lot of girls who have never met you before) she probably hasn't made a judgement about you yet, and if you speak confidently to her she's unlikely to judge you harshly (strike that, even if you talk to her and you're so nervous you're visibly shaking, she probably won't judge you harshly as long as you don't act like a total dick). And even if she does turn you down, it's not the world ending thing it feels like. Hell, if you're on a big college campus like mine, there's a good chance that you'll never even meet her again.
So, feel free to take my cognitive restructuring advice or leave it. It seems to work for a lot of people, but there are no universals in psychology, and even if it does work for you, it will still take time, work, and patients. Either way, don't give up. Things went way down hill for me when I gave up during my second year of college, I thought I'd hit rock bottom, got addicted to drugs, and found out that I had a lot more to lose than I ever realized. I'm one of the lucky ones, in that I managed to get clean, but not everyone does. So, keep your chin up and keep trying. The world is full of good and bad, but if you look hard enough you can find the beauty in it.