I am depressed, for no reason?

Im a teen, and i have a perfect family, and school. Sometimes at school a boy calls me short, which i have no problem with, but then he picks on my buck teeth, which i have, but then i start "joking", him too, which causes him to joke me, and makes my day moderate, which drops down from elated to moderate. I dont think that bullying is the problem though, I have a school counselor, but i dont feel comfortable talking with her. I talked to my mom and she hugged me and said everything will get better and told me there was no reason to be sad :) She really comforted me, but why am i depressed? Sometimes when i was sad, or scary movies, i am sad for a few days, or 3. And i feel like it never goes away. Ever :( Why am i depressed? What are the signs? Is it just hormones?