The early signs of depression usually come about after experiencing considerable stress. The early signs of depression can include irritability, being easily frustrated, sadness, over-sensitivity, negativity, sleep problems, appetite problems, and fatigue.
However, if you continue to have chronic stressors and you don't deal with it adequately, then you may go on to develop a full-blown depression, especially if you have a family member who has a history of depression. You know you may have depression if you also develop low mood, inability to have pleasure, feelings of guilt, hopelessness, and suicidal thought. If you have these symptoms, then you should see your doctor for help.