I have struggled with this, as well. My sister and I (who were both brutally abused as children) grew up with no self-worth or self-confidence; however, we both found that continuing to reassure ourselves that we are happy worked. It's kinda like the saying that if you think sad and feel sad, you'll be sad. But if you think happy and feel happy, you'll be happy.
Instead of pondering your depression all the time, think up new ways to spend your time. Take up a fun hobby, like sillygirl said. And don't forget to give yourself a hug everyday.
