when i was 9, i suffered severe appetite loss because of chrohns disease. its probably not that but if you have fatigue, loose stools, or bloody stools (stool is another word for poop) then it might be chrohns or cholitis. if you are taking ADHD meds it might be that too. at the start of the pandemic, my appetite was very small. i was barely 90 lbs. and then they took me off my ADHD meds. now, 1 year later, i have a huge appeteite and i am 120 lbs (not overweight)