Negative thoughts regarding self, future and world is a traid of depressive thoughts. These negative thoughts leads to emotions and feelings that are negative, these emotions leads to behavior (social withdrawal, etc) and these behavior again leads to the negative thoughts. This vicious circle causes depression to last long.
Next Steps
Take help from a professional.
Health Tips
try making a routine and follow it, try to evaluate it daily, try being around people and not alone. avoid taking stimulants after 7 or 8 pm. play soft instrumental music and focus your attention on it when you are in bed.