How can I stop being so intimidated by other women my age? HELP!?

I am terribly intimidated by others I don't know, esp. other women around my age (20-29)!I just lock up and act as if I have no personality when in fact I do. I'm actually really funny and personable, but for some reason, I freak out! I HATE THIS, it has caused so many problems in my life (lack of girlfriends, embarrment in social situations, etc.)I have even been victimized by mean girls just because of my lack of a "core" group of friends. I just have a very hard time talking to others, initially. I try so hard to make some kind of conversation, but most of the time they COMPLETELY BLOW ME OFF! I am 25, a college graduate, and pretty (I think so). SO WHAT IS MY PROBLEM?????????