Why I can not even think about success? While I was full of confidence before.?

I have been one of the best in education in my country, where education is highly competitive, but it is about six years I do not believe in myself and success. It is as if my mind would not like me to be successful, even when I want to imagine my success to get positive energy there is something in my mind that hinders it, I can not even see its image in my mind. The reason may not be as important as what I can do. I am desperately in need of some help. During these years I have read a lot of psychological books as well as having some sessions with some counsilers, it has all worked for me because I have been able to overcome my depression after death of my daddy, whom I love. I think even the symptoms of depression should have evaded after so many years. Can you help me with what I can do to continue my way to success in education. I always see the amount of information I do not know and not what I know. However, I do not seem so, at all and every body finds me very optimistic (I am)