Not all of us have good lives. Not all of us enjoy life. Better not to begin; once begun, better to finish.
I've felt the same way all too often in the past. In my experience, gratitude is the best cure. Being grateful for hot showers, for tasty food, for a good night's sleep, for anything good or enjoyable really, these have really helped me to change my perspective so that I do enjoy life, I recommend trying it to anyone feeling that way.