Hey, uh this is... depression. That feeling of disinterest in everything feeling like everything is dull and every happy moment will eventually go back to being dull. That's depression. But please don't take my word for it, I do not constitute a mental health professional, I'm just speaking on my own experiences.
You should talk to someone about this. Your parents or something. If you can, of course. If you can't, you can always come here or so.