How can I treat myself alone from anxiety?

I feel too nervous to go out alone. When I see people’s faces, I worry on what they are thinking about me although I don’t know them. I experienced difficulties in making new friends and socializing with others. At school, I’m always alone and so quiet. I want to join my classmates but I feel afraid that they might reject me. I also find myself avoiding eye contacts at someone I’m talking to. These days, my sister also noticed that I sleep excessively. I surfed the internet and I felt afraid when I knew that I’m having symptoms on anxiety and depression. I don’t know what I should do because I can’t just tell this to my parents.