This is a very common condition prevalent among younger people. This condition is called inferiority complex. Specially after the boom of social media and increasing importance put on financial success, many people see all good things and great things which makes them feel unfulfilled and reduces their own self confidence.

You have to overcome this kind of feeling by focusing on positive aspects of life and by putting things into perspective. You will never be satisfied with the amount of money because there is always more to have. Appreciate what you have such as your family, friends and the love you get which is priceless. You don't have to judge yourself harshly or try to compete with others. Just believe that you are a special person and stop comparing your material possessions or looks in order to feel good about yourself. Build your confidence. Read books on philosophy or other self help books that encourage your confidence and outlook on life. More than anything you need to change your outlook on life and understand what is important for you. Change your priorities one step at a time. You don't want to worry about what others think about you. Most of the time, other people are busy with their own problems so do not restrict yourself thinking what others with say.

Another thing is over thinking. You probably think too much. Although thinking resolves a lot of problems, most of the time, thinking is not productive because you end up worsening your state of mind. You need to be in control of your mood. You are the reason you feel bad because you start thinking all the negative stuff. When negative thoughts come to your mind, you have to actively push it out and think something else or just keep your mind blank.

Hope this helps.