Hey. I understand why your doctor says that you're like that. It's completely understandable. Leaving your friends and moving schools is always hard. Being the new kid, not knowing how thing are, getting used to it... Everything is a huge impact.
I think that you shouldn't give up on finding friends, that always takes time. It's hard to meet somebody and find that thing that makes people click together. It takes time and effort. Yes, perhaps you didn't have successful relationships with your peers in the past, but they're just a few people and the world is full of people.
You should join a club or something where you could meet more people; something you enjoy where you could find people with similar interests and meet some potential friendships. How about something related with skateboarding? Video games? Doing some volunteering.. There's always ways!
Maybe you should also consider being a bit more lay back when it comes to people; by this I mean being yourself but avoid cracking up on people for little things. You should talk with your doctor about this type of things and ask him to suggest you some tips; after all he's an expert, he knows about this type of things.
Your old friend, why don't you invite him to do something? A movie or something you both could enjoy. It's going to take effort because you're not as close to him as before, but if that's what it takes, so be it, make it happen!
Also, I'd suggest you that if the school you're in is making things to hard, maybe you could consider changing schools? Although that might bring you back to the start, but It could also give you the opportunity to start again.
Good Luck!
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You'll never get to heaven if you are scared of getting high.