I understand why you are frightened. I don’t understand how it is that you’ve been able to isolate yourself so severely since you were 13. You didn’t mention what your parents have done or not done about your behavior. I hope you are keeping them informed of your feelings and that they can be supportive and take the needed steps to get you the help you deserve.
Without more information, I have no way to determine if what you are experiencing is the result of a sleep disorder (which I suspect is at least part of the problem), social anxiety, depression or some other problem. I do know that you can’t handle the situation by yourself. You need help. You need a proper evaluation of your sleep habits, your diet, your general physical health and your mental state.
The place to start is with your regular primary doctor. I believe that Serbia has been working on reforming mental health services for almost 20 years. Your doctor will be able to refer you to the appropriate professionals.
Adolescence is tough for a lot of young people. You are certainly not alone in withdrawing into your room. But feelings such as you describe should not be ignored or untreated.
You’ve already lived with this distress for 3 years. There is no need to continue feeling so terrible and so afraid. Please come out of your room and out of your own head and reach out for the support that is available to you.
I wish you well.