These should be behaviors that they do not normally display, in other words, it must be a change in their behavior. Doctors aren't sure what causes depression. But, the reasons teens get depressed are varied. It may be something different for each person. It could be caused by stress over school or relationships.
Some teen girls become depressed when they go through puberty.
Their depression may result out of a difficulty dealing with their changing bodies. By the age of 14, teenage girls are twice as likely as teenage boys to have depression. If your child displays the symptoms of depression for longer that two weeks, you should seek medical help. Your pediatrician is a good person to start with. He will probably run some tests to confirm that the symptoms are not caused by an illness or an infection.