When I feel super apathetic and unmotivated, I FORCE my pathetic butt to do stuff. It's quite difficult and you have to try to lift your mood at the same time. Some stuff that helps is

-taking a walk
-cleaning up a bit (sense of orderliness=happier)
-exercise (running, once you're out and away from house, you have to keep going haha)
-reading (escape to another world)

Don't forget to eat. Eating right can affect your mood.