Maybe it's your confidence, or maybe you're looking for the right person. Everyone makes friends and boyfriends/girlfriends differently. Some people just hang out with a large group of people that they call friends. But are any of them really CLOSE friends? Not necessarily. Other people have a few friends, but all of them are extremeley close.
Then there are people like me that sit there and wait for people to talk to me first :P. I don't take the initiative, and because of that, I don't make friends unless they say something to me beforehand.
So part of it can be from your attitude, but I don't think appearance would have any role on your ability to make friends with guys. If it's something that truly bothers you, then change it. You may not change over night, but you may find it's not so difficult. If you have a friend that has friends that are guys, then you may easily be able to make a friend through another friend...
I wouldn't be depressed about it... instead, look towards how you want to change it and what you may be able to do :). You may find that starting a simple conversation with someone in a class over a homework assignment might get you somewhere... who knows.