[chriseidhof]

A book that really helped me is Flow by Csikszentmihalyi. You probably can recall a moment (for example, when programming) where you were in a state of flow, you were solving difficult problems (but not too difficult) and everything just went naturally.

His book is about this state, and about how to reach happiness in general. The key point is not only to depend on happiness as told by external people (e.g. parents, girlfriend, government, boss) but also create your own triggers. It might be making music, looking at a sunset, etc. In other words: be in control of your own happiness.

That being said, I think it's wise to see a professional. Ultimately, you'll have to do it by yourself, but they can help you get back on track and provide guidance and pointers. After all, it's their job.

Good luck!