Take quiz/see doctor
Most people are occasionally depressed, but there are clear criteria doctors use to assess clinical depression
There are good online quizzes at http://psychcentral.Com/depquiz.Htm & http://counsellingresource.Com/lib/quizzes/depression-testing/
if you feel depressed consult with a psychologist, psychiatrist or family doctor. While medications may help, i advise a holistic approach to treatment.