Taking action! There are medications and other medical treatments. In addition, there are psychotherapeutic interventions that can help. Beyond the professional treatment angle people could get more active with others, count their blessings, exercise, do other healthful behaviors. There are new scientifically-based books on increasing happiness as well. But taking action is what will help your depression.
Depression. Initial evaluation by mental health professional to confirm diagnosis & recommend treatment, such as counseling, medications & life style changes.