Feeling out of the loop

This might be the wrong thread for this forum, I'm not quite sure, so apologize in advance if so. I'm not quite used to roam this site but I figured this might be where I could ask advice for something that has stuck with me all my life.

It's really weird but I always feel like being out of the loop by everyone, I guess. I don't really mean feeling left out by a particular group of people/friends though. It's more of a feeling like everyone in the world is in on something and knows about something that only I'm not privy to. I know this is completely irrational. I feel borderline paranoid because every action I take, every phrase I say, there's this voice in the back of my head that says: what if what you're doing is terribly, fundamentally wrong and everyone already knows about that, everyone already knows not to do this but no one bothered to tell you, because of course, you should already know this.

A simple thing like buying a shirt with a harmless design makes me overthink that maybe there's something really, really embarrassing or insulting linked to that design and that everyone is going to laugh at me or judging me wearing it. Like there's this inside joke every person knows about but not me. Like there are a bunch of unwritten rules in place that everyone is obeying and I try my best to do it too without knowing what those rules are.

There are simple things I cannot do because I fear that the slightest misstep will ruin everything. It takes me three hours to write my friend that yes, I do want to meet up with them, because I rewrite this simple sentence a hundred times, each time finding something new that might give off the wrong impression. Do I sound too cold writing just 'ok'? Too cringy when I sent an enthusiastic reply? What is the 'correct' thing to send?

It has gotten a bit better over the years but I still can't shake this feeling. I wanted to share this to see if anyone else also has this feeling or if there's any advice on how to ignore this.