I can't understand why I am so unhappy with life?

A lot of the time when people are depressed for no apparent reason it is because they have a chemical imbalance in the brain. Antidepessants can fix that. You should speak nto a therapist to see if you need medication or whether it is something else at the root of your depession. Check out "depression self help" and "natural cures" at www.depressiondodging.com for some tips on dealing with depression.