Re: Social anxiety resulting from childhood ostricisation
I moved as a child a lot (military father) and am already introverted naturally, so the two situations (moving and being introverted) was not a good combo. My social-butterfly sister thrived in it--I did not, and as a girl myself it's "weird" when girls don't talk much.
So I grew up to be the same way: socially anxious, not knowing how to approach others, aloof in unknown groups of people (it's worse when they all seem to find instant commonality making me feel even more alienated), feeling judged as "that weird quiet kid", lost in my own thoughts in my head finding comfort in my preoccupations, etc.
I'm 39 now and I'm not so bad at it anymore. Quite simply, it took me time to grow into myself and become a better quality of self-aware. (I was already self-aware, but painfully so.)
For me, it took going at it blindly without anyone to talk to about it (no internet when I was your age) so I would say you are at a great advantage in finding a faceless group online to talk about this in a supportive way. But try to limit this to groups designed for giving advice for taking action, because the temptation will be there to find an online social group and spend all your time there, removing yourself even further from society... that's not good.
I'm not going to give you any social setting tips, because if you're like me in this aspect, too, everything (everything!) is "easier said than done" And I think you might appreciate that. And by these tips, I mean like "When at a party, try wearing a funny tshirt." or "When in a new situation, think of something witty to say." That's all dumb. Those are tips for people who DO NOT have life-long social anxiety and are trying to break ice with new people. Well meaning people give people like us advice like that, even though we see it as a painful reminder that most people really do not understand the actual problem.
What I wish I knew to do when I was younger (I hope this helps you) is to sign up for a class doing something low-key fun. I don't mean a college class where performance anxiety might cloud the situation. I mean a hobby class like building things, or cooking, or exercise, or drawing, or even musical instrument. Try to avoid hobbies where crazy hyper-socializing people will be, talking 50 miles an hour about their relationships and parties, etc.
Then go to this activity with no expectations other than to work on learning your hobby. Soon enough you might find yourself making connections. It might take a while, so don't worry.
I think in the long run, you may just need practice like I did, using planned environments to hold me up. For me, the anxiety came from the unstructured nature of social settings. "What do I talk about? What do these people talk about? How do they make it look so easy? Do I fit in? Are they looking at me wondering what I'm doing here? They talk so fast about topics, I can't think of one!" And then I'd lapse into daydreams to escape (or want to lapse into daydream, but couldn't because I was desperately trying not to be "weird" which made it worse.)
Those worries are lessened when you have a clear purpose for being in a situation. That can give you time to work on learning to socialize with structure, so when it's time to advance to parties or events for the sole purpose of socializing (yikes!) you'll be practiced.
And I know it seems far off and maybe useless to hear right now, but as you grow older, you will also become wiser, more experienced (if you just keep at it!), and more receptive to alien social situations.
I hope my insight can assist you, along with any other advice from people who experience social anxiety can give you. Lastly, avoid getting advice from well-meaning social people who don't have any experience or education on SA.