Now I am no doctor, but I think everything you describe sounds like anxiety. I could've written that post 20 years ago. When I was diagnosed 2 years ago I was surprised because I was sure I had ADHD or something more complicated. At least in my situation the more I read about it, it seemed that was my problem.

What helped me when I was in your shoes was get a couple books to help you get in a better space mentally. I found hope and help for your nerves and a cognitive therapy book were godsends. Remember I didn't know what was wrong or I had anxiety but they helped me get out of the funk. Being this was 20 years ago, something newer might suit you better. I didn't think I'd be able to read a book because I barely could make a phone call. Reading a book that was accurately describing what I was going through was enough to stick with it.

I'm sorry your dad and sister don't seem to take your pain seriously. That is common with people who don't have depression, anxiety, or the like. It's hard to fully understand how hard things appear to someone that does. Your sister sounds extremely young. I don't have much advice other than to ignore it, which can be hard.