I definitely hear what you there, I've always felt extremely out of place whereever I went unless there was a shitload of drugs involved and people looked up to me for my vast knowledge about them. Never really had any problems to acquire friends at all, but the social awkwardness is a perma-guest in my brain, even when I come off as most confident. What people said about weed is in MY experience true. It makes social anxiety so much worse. I've only ever smoked at nighttime, but even the "hangover/afterglow" can increase social anxiety 100-fold. Worst drug ever when it comes to that, though some people seem to be spared from that "side effect".
Anyway, if you want pure practical advice... Get into social engineering, learn how to dominate a group. There's a shitload of pickup artist and NLP reading to do on the internet, it's fucking crazy. Teach yourself some basics about nutrition and exercising, start pumping iron (really lightly though, you're 15 and don't wanna do any damage), eat adequately and respect your body or if you don't, respect it's looks at least lol. It sounds pretty dull and lame, but this shit really works if you have the motivation for it. I'm not saying get on androgens and turn into a monster, just keep a healthy appearance. People love that. People are scared away by insecurity and friend-seeking behaviour, you might have been displaying a lot of that and had the very problem you're tring to solve working against it's own solution.
I really know how lame this plan sounds, trust me, but it's a sad truth that these are the things people go for. We all just want a strong social network giving us security and a person that displays health and social skills, especially at your age where money comes second, means social security for people. If you decide to go down that road (close to all bodybuilders have once found themselves in a similar spot as you btw), you can establish a stable sense of self worth for yourself during an episode of life which is critical for everything that comes after. Just be aware you might be scaring off some of the intellectual crowd, but who needs superficial judgmental fucks like that anyway, right?
Oh and regarding seeking a psychiatrist... DEFINITELY go for other options first. There's so much to be done about how you are feeling just by teaching yourself about how people roll. I remember the Venusian Arts Handbook written by a whackjob called Mystery being a key read for me once lol. I couldn't believe how easy it suddenly seemed to get pussy. I do admit the social anxiety lasted through all that, but part of that is really a physiological reaction to how well you are navigating in your social environment. Not very well I'd assume.
When it comes to seeking therapy, that'd be a better place to start imho. In which case you should probably prefer behaviour therapy if you want relief of social anxiety over figuring out what moment in childhood makes you weep the hardest.
Edit: I just read DXM triggered said anxiety? For an extended period of time, long past the actual intoxication? Might want to check up on diagnostic criteria of bipolar disorder, too. There's tons of tiny symptoms and abnormalities hinting at it and you're probably best of reading up on it yourself. While I definitely wouldn't consider going on meds if such a condition should actually be diagnosable, it might help you to understand yourself and potential future "changes" you experience much better and also allow you to cope with them or avoid their exacerbation. I might just be reading my own history into you here, since it took me 30 years to gain a diagnosis despite being quite knowledgable in the field and having been in treatment for a whopping 8 years, 4 of them spent in multiple weekly therapy sessions without reaching a diagnosis. I considered everything, but not THAT.
Edit 2: DO NOT get on benzos, even if some moronic doctor tries to prescribe them. Imho your reply should come as a punch in the face to him. Too many lives ruined by those god-awful sedatives. Ask anyone on this board who has been on them and they will tell you the same thing. They just don't help very well in the long run or can even be counter-productive.
edit: me silently thinks youll definitely become a bad-ass bodybuilder :D
