I don't know if it's worth looking into irritable bowel syndrome. I have a friend that sometimes feels nauseous when eating and its down to that. Do you need to go number two more than once a day? Do you often have stomach ache/gas etc if do could be that
Maybe nervous energy is ruining your appetite, or maybe activity is just masking a problem.
I used to have a terrible appetite, and it turned out to be constipation and Celiac disease. So don't brush it off. Make sure you see your doc for physicals and mention the poor appetite just like you described it here.