Find something fun about working out. That’s what you need to do, you need to find out what is fun about working out. You say “nothing!” but I say sure there is something. For cross fitters, its competing against yourself and being able to be in an environment where it’s encouraging and uplifting others. For power lifters, it’s being able to continually put up more weight, lift heavier weight. For runners its freeing your mind and being able to let stress out. For boxers its hitting something and letting stress of life get out. For body builders its therapeutic and able to sculpt your body. So you have to find an aspect to fitness that is fun for you and you can find it.