This is a fairly common problem that young people like yourself experience. One way to deal with the situation is to re-evaluate the past and understand the factors that might have interfered with your ability to focus and work hard. Also try and do a goal setting exercise where you try and figure what you would like to be 5 years from now, 2 years from now and finally a year from now. Then work backwards and identify the steps you need to take to accomplish these goals. The only way to feel better is to take control of the situation and even if you take small steps now you will be able to counter your negative thoughts.