In this video Dr. Joe Dispenza discusses the why behind being unhappy and what can be done to change it. I really like this because he demonstrates that you can change your mind and you do not have to be unhappy.
There is a very interesting piece about how there is a refractory period.
Basically there is period where a mood changes into your temperament. If you stay attached to that emotion too long, it then changes from temperament into your actual personality.
One way to shorten this period is through meditation.
If you have been experiencing a bad mood for way too long, this is worth watching.
Let me know what you think.