Therapy won't get to the root of the problem, its more like changing the way you think rather than adressing the issue itself, if you cant think of a reason as to why you're unhappy then I would see a doctor as it could be a hormonal problem. If you know there is something in your life that is causing this, sort it out yourself and if you can't... youll just have to get over it.. near enough everybody will experience some form of depression at some stage in their life.