Exactly what Jarett said - it might not be you. I am one of the many guys who are too nervous to approach a girl even if I am interested in her. Plus too the "goody two shoes" is a little intimidating. Most guys like a girl that is good but with a little bit of a wilder, bad side.
If guys don't usually ask you out, it's probably because of your personality. MOST guys don't like very prude girls who have to live up to Mommy and Daddy's expectations all the time. If you're mean, almost any guy will not be interested. The last thing a guy wants is someone who has a "nasty" or bitchy attitude. That could be your problem. Not to bash on you or anything, but that's just from what I know.