Hi, I'm 16.
First of all, I'm seeing psychiatrist for two years because of depressions, and neurologist because of chronic migraines (I have problems with attending school because of this - I'm usually at school five or six times a month).
My oldest brother has died when I was 4. He was taking care of me and I loved him very much. I felt very anxious when being alone after that until I was about 10 or 11.
Now I feel anxious when I have to be or talk with other people. It's not that bad with my family (although I sometimes feel bit anxious to start conversation with my parents). The two worst places are bus, where I feel like everyone is starring and laughing at me and school. I HATE talking in front of class, even if it is just one word, I never raise my hand even though I'm sure that I know the right answer. I don't talk with classmates and I really don't like when they're asking me about something. I also hate sitting next to a stranger in bus or cinema.
I never really spoke to my psychiatrist about this. She has just told my mom that I'm introvert. She judges so because my hobbies are programming, watching movies and lonely walks in forest, where I don't meet anyone. It hasn't really changed since I'm seeing her.

So, is there anything I can do? I know it's not normal, but I just can't help it.

You'll just have to keep challenging yourself to move past the uncomfortable situations.

Tell yourself today that "I will raise my hand and answer (even if it is wrong.)"

I tend to be on the introverted side in person but am opinionated online. Find an outlet that allows you to work through your issues. It doesn't help that you are 16, too. It gets a little better the older you get.

Sorry about your brother.