I always doubt it. What happened?

First of all, you are extremely insecure. Secondly, you may see or hear a lot of bad things, which leads to your distrust of the whole society. Now you should adjust your mentality, believe that the world is beautiful, explore beautiful things with your heart, try to get along with your classmates and friends, communicate with your family more, and have something in your heart. If you can't find someone you trust for a while, you can write it out or post it online, so that everyone can help you out of the predicament. Remember to always believe that you can do it, and don't be discouraged even if you fail.