Roughly he human body is 60% water.
Showers make most people feel better, because it clears out sinuses and you head. helps increase or decrease body temperature (since when a person is too hot or too cold it effects their mood), and gives them that alone time they need in a calm quiet environment, to think. When your done, it's refreshing and calm; sorta like washing away worries.
Swimming helps, because bodies of water are calming, and they make the body feel less heavy, will causing a person to exert themselves. Any kind of physical activity will help encourage endorphin release (endorphins being the hormone that causes happy feelings). And again, it gives you time in a relaxing environment to think.
Besides that, a healthier diet (less fatty foods, more balanced) tends to do wonders on mood and motivation.
Severe lack of motivation for a long term period of time is a symptom of depression (even if sadness isn't associated with it in any way) and it would be wise to consult with a doctor, and see what you can do. (Avoid antidepressants, then tend to really screw with your head)
Other things I can suggest is writing down thoughts loosely, give yourself 5 minutes where you have to write nonstop, whatever comes to your mind, even if it makes no sense, and just write it all out. Talk to someone you trust about anything that's been on your mind, or take some time off, doing nothing that you would normally do in a typical day, maybe take a weekend to get outta town; go camping or something. The break from the usual routine can help break up feelings of each day being the same, day in and day out; this causes lack of motivation too..
Other than that stuff... I think of others expectations of me, and my desire not to fail them, but I don't usually have too many problems with motivation anymore =3