What you need to do is this - whichever one you feel closest to, try and arrange to meet up with her on her own, for a drink or something. And then just say you feel like you've been pushed out slightly and its getting you down. See if theres an actual reason for it all.
Have your friends ever seemed the type of people who would just push someone out of the group for no real reason? If so, you're probably better off without them because I cant imagine how crap it would feel not knowing from one day to the next whether your friends still want to know you.
And if they arent like that, then you just need to find out what the issue is. Could you have done anything wrong to annoy them?
Edit* - dont feel too down about it like you're socially retarded or something. Most people get this done to them at some point, although generally there's a reason for it, people just need to communicate more instead of ignoring problems!