Hello!
That's an uneasy feeling to feel left-out. When you look back, what has recently happened? A fight, gossip, new boyfriend? Among those friends, do you have one of them that could be very honest with you? The whole truth and nothing but the truth?
I have found these articles and they really help, so I thought it'll be appropriate to share them with you. Feel free to contact me whenever you want.

Why Don?t I Have Any Friends? | Young People Ask

Build Friendships and Fight Loneliness | Teenagers

How to Fit in and Make Friends | Teenagers