How do I stop depression?

I think I'm on the verge of depression and I want to talk to a counsellor but the school year is over. So that's why I decided to ask here. If I tell my parents they won't listen. The little things tend to bother me. I have low self-esteem. I think I'm fat and ugly and no one likes me. If I were to disappear, no one would care. That's the mindset I have. And I know it's wrong but sometimes I can't help but think that way. I haven't been brought up in the best way so I'm not always the happiest person around. Finally, I sometimes think about death and how the quickest and painless way would be. I don't know what to do. How do I battle these depressing thoughts?