I'll join Quirky in regretting you have waited so long for a reply. We wish the system worked better, sadly sometimes it lets us down. There is nothing about you or your post that caused the delay. It just sometimes happens.
So if are still reading here I'll try to offer some thoughts. I've read your posts, they go back over a couple of years, and deal at least in part with how you see yourself, and how you think everyone else at school sees you.
You do not regard yourself yourself well at all, which is a pity, you come across as a caring and sensitive person with a conscience
This then came to a head where you made some remarks about your brother in an attempt to be funny - which you feel see was a mistake.
OK, maybe it was, but not a big one, humor sometimes works, sometimes not, then it can appear unkind. There is a huge difference between a few words and actually being unkind, and treating your brother badly. A learning experience, but not something to fret on for too long.
Actually what has being going on for too long is feeling uncomfortable with others , and imagining year 12 students have it all together, and you by comparison do not. This is no way to live. You need like everyone to be happy and feel supported most of he time.
So now it looks like you are in retreat, staying away from social contact, and feeling unhappy. If life with others is uncomfortable, you feel criticized or regarded as less than every one else. Then to avoid those situations and escape into the worlds of YouTube and so on is very understandable
Not good long term though.
May I suggest you go back to your doctor, or if that is not practical see a school councilor and say that is happening and things do not seem to be improving.
Perhaps you would be more comfortable phoning or web-chatting to the Kids Help Line (1800 55 1800) or https://kidshelpline.com.au/get-help/webchat-counselling/
It's pretty good, sensible and realistic and very used to dealing with these sort of problems and can be a start to feeling better.
What do you think?