It happens. Cliquiness is the way of things, particularly at your age. But you can get some humor out of it. Try watching "Heathers." It's worth a laugh if the laugh helps you to see those girls in a different, better light.
The age old problem. This always hard to answer. Being a guy, I would say take the aggressive approach and humiliate the the lead chick somehow, but that may not work for you. Maybe you will get lucky and you have fallen off of their radar.