You know, I have a similar problem as you... I found out I had Seasonal Affective Disorder (SAD) which gave me a type of depression... it really sucked, I'd get depressed over nothing, but smoking helped take my mind off things too...

If you're the kind of person who can stand to research stuff, here's a couple links of crap that helped me. Just skim it over and see if the effects fit you:

http://en.wikipedia.org/wiki/Seasona...ctive_disorder
http://en.wikipedia.org/wiki/Dysthymia

If that doesn't help... good luck man, I found out how I could make myself happier, I'm sure you can too. And keep smokin Good for the soul