Things have changed so much at school. I feel like leaving?

In my freshman and sopre years, everyone was part of a big crowd and we just went through everything together. We hung out together, ate lunch together, etc. But then starting our junior year, the guys still hang out together but its like the girls kinda broke apart. Each girl has a group of 3-4 friends that sit together at lunch and hang out after school and on the weekends. The girls that I used to hang with the most either have found their own little group or are in serious relationships now and spend most of their time with their boyfriends. I talk to alot of people in school, but I really don't have anyone to hang with outside of school. I feel like I'm not particularly close to anyone and that I'm missing out on the closeness of friendships and having fun I've tried talking to new people, but it seems that everyone already has their circle of friends and are not interested in bringing anyone new to it. My old friends always talk to me about their crazy weekends and such but never invite me to do anything with them. I really feel like breaking down and crying... like I have no one to really talk to. I asked my mom to let me switch schools, but she warns me that sometimes when you switch schools your credits don't transfer and that would really backtrack me in school, considering I should have my 24 credits at the end of this year. What can I do? Is it worth a transfer?