My 19 Yo Son Has No Appetite, Multiple (6+) Bowel

My 19 yo son has no appetite, multiple (6+) bowel movements daily, not diarrhea, insomnia, anxiety, fatigue, weight loss of approx 15-20 lbs without intention over past year. He is 5'11" and weighs about 130 #. He barely eats anything, probably less than 500 calories per day, feels a little hungry but nothing appeals to him. He was prescribed Paxil for anxiety which made him feel awful and ambien for sleep which did not help much. He rarely get more than 4 hrs of sleep per night. He smokes marijuana to try to make him hungry and even that doesn't work. His recent blood work showed mild anemia.