Bullied at school?

How many people having social anxiety where bullied at school?
Is this the reason you have social anxiety?
For me, yes. I think that is one reason. I was bullied at school.
Now, as grown up always I see a group of people I feel the anxiety. I start shaking, sweating and are so affraid they should start laughing at me. All the time. I can feel my legs freeze and can baraly move, which make my movement seemed weired witch causes unwanted attention from other people. This is a reaction in my body I can't control myself. I don't know what I could do, so I can walk normaly when I see other people. This probaly sounds very stupid. but at the same time I think that many people here suffers and have this same problems.

I think being bullied is part of the reason.

I get along well with people for the most part. I've come a long way over the last few years when it comes having confidence and being proud of who I am. That being said, I still find it incredibly difficult to make friends/relationships. I still remember the unpleasantness of school days and I guess I've developed a defense mechanism of sorts. I tend to shut people out before I even let them in. I'm also very suspicious of people when they try to befriend me, almost as though they have some hidden agenda. It really takes me a while to drop my guard and open up to people.

In some ways, I'm my own worst bully.

You say you can't control yourself but you can, you just haven't mastered it yet. I advise you to read The Happiness Trap by Russ Harris. It's a pretty great book on how to handle your thoughts and how you process them.