I wouldn't worry too much about it if I were you. Around your age I experienced the same kind of lack-of-feeling, a year or so later so did a friend of mine. However it passed for both of us. Retrospectively I suspect a great deal of the problem was that neither me nor my friend had invested time or effort into anything. Try working on something or executing a plot, also read http://lesswrong.com/lw/bq0/be_happier/ .

Also, reading good books works.