Yeah i felt that way a few years ago when i had some depression happening. I think it was partly the depression, and then partly the medications - they seemed to desensitize me even more. Try to just keep doing stuff you enjoy, or that interests you at all. I kept finding i had no interest in things i thought i was meant to - things other ppl were loving and laughing at, i'd just be sitting there uninterested. Instead of comparing your reactions to other people's, just compare within yourself - which things do you enjoy a bit more than others, which things to you find less boring than other things. Like Lost Girl, i found it was usually some old favourite movie, tv show or book that i still enjoyed, and just staying in touch with those things was enough to keep my mood going along alright.
Exercise can be pretty good too - sport, or just jogging, gets some adrenaline and other good hormones flowing. Even if you're not feeling much emotionally, or psychologically, you might get some good physical reactions going from exercise.