Depression - Teen Support Group
Teen depression is marked by persistent sadness, discouragement, loss of self-worth, and loss of interest in usual activities. Depression can be a temporary response to many situations and stresses. Teens may be more susceptible to depression due to the normal maturation process, the stress associated with it, and conflicts with parents as they become more independent.

I personally go through periods where i feel confident about myself and that i'm a winner and i can do it all and within a matter of time i start questionning myself and my ability to achieve my goals. Today was actually one of those days. But i keep positive thoughts in mind.
Here's asaying that I like : "Someday soon, you will find freedom from this darkness.And when you do, youll look back on these days and wonder how you could have doubted your resilience.
Youll look back and marvel at how something as small as refusing to give up could transform your life in such a substantial way."
~Daniell Keopke