When I become unmotivated in things which is important to me, job, learning, my hobbies i notice that the main reason is bad mood, or depression. And lack of interest is the only consequence of that, i read somewhere what old Greeks have practiced, period of hedonistic life, and after that period of ascetic life. Human beings work like that, nothing isn't good when is to much, or by force. I suggest you little change in lifestyle. Some physical activity is crucial, and healthy food.
