i think I have PTSD. I don't feel like anyone understands, and have shut myself away. The world is not a good place, it is full of pain and it's overwhelming.

The world is full of pain, however, pain makes us stronger. In times of difficulties, look for the helpers. There is always someone helping, someone working to fix the world and make it better. It doesn't sound like you're very happy with the world - you are right that it is not always a good place for some people. Perhaps you could channel your feelings into activities that contribute to making the world better. You could try to help the homeless or underprivileged people in your area, stray animals, young parents...the possibilities are endless! In the meantime, try to see a counselor.