I'd suggest start talking with people you don't normally surround yourself with but know at least a little. Be outgoing and just act like you normally would with your friends. Get yourself out of your comfort zone even if that means being a bit uncomfortable. You need to face the issue in order to overcome it. It can be hard at the start, but practice makes master, so just put yourself out there and start working it.
Perhaps you stress about being judged subconsciously and that's why you avoid saying/getting yourself into that type of situations. It could be a mix of shyness, social anxiety, etc.
You don't need to be friendly with everybody, of course you can be a private person, and that's perfectly normal, but as you describe it; it seems like you avoid talking with other people (Outside your friendship zone) and that's not healthy. You need to fix this because it can great impact in your future relationships and life in general. (As human beings we need to socialize.)
Is this causing any problems in your daily living? Because if so, you should/could talk about it with a counselor and see what they'd recomend. It's not that uncommon for people to have this type of things, In fact the number #1 fear human have is talking in public.
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My inbox is open if you want to talk.
:)
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I've got a hunger. Twisting my stomach into knots
That my tongue has tied off.