I had kind of the same progression in school. My family moved almost every year until I was 8 years old and just about to start 3rd grade, when we moved to an extremely small and very religious conservative town in Indiana. This place was the closest I've ever seen a real place come to being the way small towns are depicted in horror movies. I'd been raised by intellectual parents in an academic environment, playing D&D and reading Tolkien... so the odds of fitting in with this place were very stacked against me to begin with. Then my parents told me that we were probably going to live there for the next 10 years.
I went absolutely haywire over the idea of being able to make friends and actually keep them, and turned myself into the class clown for the next 5 years or so. No friends. Not much true bullying, but general unacceptance from everyone. Around the beginning of 7th grade, I was getting so desperate that I started hanging around dangerous losers who used me as a tool. I also started to calm down a bit. I was around people more so less lonely in that sense, but starting to suffer real abuse and still had no real connection with anyone. Around the end of 8th grade, I started deliberately alienating myself while making real friends online. High school was very rocky. I started getting rebellious. I got hurt a few times, though I chose never to hurt anyone else. It would have been a lot worse if I hadn't started over at a new school my Junior year, at which point I very consciously became almost completely anti-social, because I just wanted to finish my last two years without trouble. It was here that I got very good at avoiding attention.
I've never had any serious issues requiring professional help, even though some people used to think I did. I overcame everything on my own. I get along with people just fine today (I'm 28). In fact, I can get along with basically anyone, including people like you who have trouble getting along with anyone.
It's hard to provide real advice without actually knowing you, but it should be pointed out that both sides of the Be Yourself vs Learn Social Skills debate are correct to an extent. It's up to you what constitutes who you are, but it is true that you can learn social skills that will help you without drastically changing yourself.
In my case, I still have bad posture, still sit in wierd positions, still fidgety, still tend to avoid or cut through small talk, among other things I'm sure I'll think of later. I can't change these things without feeling too much like a different person, and I still get comments from people about them. However, I've also learned how to appear relaxed, recognize boundaries, make appropriate eye contact, be cordial even without small talk, express appreciation or respect without seeming wierd, and navigate conversation very tactfully. Even people who are completely the opposite of me in most ways find me likeable, such as my wife's heavy-handed southern baptist conservative military veteran grandparents who apparently went around to the rest of the family saying all kinds of good things about me after they met me.
If you think you have a genuine problem, it's probably best if you at least try professional help. Otherwise, it just takes time and practice, and I don't know of any hard rules or very specific pieces of advice that would be helpful (not without knowing you, anyway). It does get better after high school for most people, but that's only if you work towards it. Don't listen to anyone who says there's no reason to believe that, but don't take testimony that it does as reason to just wait for it.