I agree that it sounds like Depression but I differ on what I think you should do about it.
Presuming it is Depression, then the main treatment approaches are anti-depressant medication, Cognitive Behavioral Therapy (CBT) or a combination of the two. I can recommend this excellent website here as a starting point for learning more about the treatment of Depression.The recommended sequence of treatments to try is:
1) Self-help using a CBT based program
2) CBT with a therapist
3) CBT & an antidepressant medication (usually a Selective Serotonin Re-uptakeInhibitor)
You can confirm that this is the correct order by checking these treatmentrecommendations here.
CBT is a psychotherapeutic approach that aims to solve problems concerning dysfunctional emotions, behaviors and cognitions through a goal-oriented, systematic procedure. Treatment is technique driven, brief, direct and time-limited (normally 10-12 sessions). CBT is used in individual therapy as well as group settings, and the techniques are often adapted for self-help applications. I wouldstrongly encourage you to consider CBT as I would expect you get great benefitfrom this approach.
Start by working through this excellent CBT based self-help program here. It should take several weeks to complete, is completely free and will teach you everything you need to know about Depression and what you can do about it. Alternatively, you could take a look at a book which will teach you some introductory techniques for dealing with Depression at home. I can recommend a well known manual titled Mind Over Mood and another book titled The Cognitive Behavioral Workbook for Depression; A Step by Step Program as good places to start. You can find them both here.
If you find you aren't making the kind of progress you would like using a self-help approach I would then recommend you consult with a CBT trained therapist. CBT is usually offered by Clinical Psychologists (although not exclusively) and you can contact the American Psychology Association (APA) for assistance with locating a Psychologist; take a look at the APA locator service here. You can use this to find Psychologists in your area and there is a phone number you can contact if you want a referral arranged for you. Also, take a look at an article published by the APA here. It's an interview with a senior Psychologist and covers some of the things you should consider when you looking for a Psychologist.
If after consulting with a CBT therapist you are still having trouble with Depressionthen you should consult with a Psychiatrist about commencing an anti-depressantmedication. Consulting with a GP/family doctor is fine to check that there is no underlying medical problem but for a treatment involving psychiatric medication you really should consult with a Psychiatrist.
I hope this has been of some help. Please let me know if you have further questions or would like me to clarify any part of my answer.