I've been in a very similar situation, all of which unfolds at exactly this age. As you grow older into your teenage years, I find that you become more conscious of your decisions and you start to understand how and why things are happening to you. From reading what you've already said, I do agree you have depression, however the symptoms of depression could also be the ones of anxiety. I went through anxiety almost all my life, it wasn't apparent to me until the ages of 14-15, when I started to be extremely self cautious, started missing school and ultimately hating life.

There are many things you can do about this. I don't know you well enough, or were you live or how your financial situation is, but telling your parents in my opinion should be your first step. Assuming you have loving and caring parents, sit down with both of them and explain how you truly feel. Ask them if there are any therapists you could visit. (I highly recommend therapy). If you are unable to do therapy due to you being uncomfortable, or simply lack the funds, there are still many things you can do to help yourself.

Firstly, do things that make you confident. Are you good at art or music? Practice these types of things daily, or every other day. Becoming more confident doesn't always mean you have to go out and make a million friends, join extra curricular activities at school that you enjoy, because most likely you'll meet someone with common interests. If all of this seems too hard for you to do, this may sound silly, but just stand up straight and smile. Walking with purpose can go a long way.

tl;drbook some therapy sessions, do things that you are good at, stand up straight, do things you enjoy