First, look into http://en.wikipedia.org/wiki/Dysthymia . Second, large parts of my family consider emself to be hardwired to be just not very happy, on the left side of the hard-wired-to-happyness-bellcurve. We pretty much resigned to it. Third, are you sure, by written review of your mental states, that your thoughts are consistent? There can be really really subtle differences; when I review my mental state I need to use more criteria than reasonable/unreasonable.