No interest in eating. Any advice?

It could be so many different things... Including those you listed. Try to get him/her to the Dr as soon as possible. My mom was dropping weight for months...barely eating... Saying she just wasn't hungry and she felt full after a couple of bites. We tried serving her her favorite foods, pureed foods, things she could easily digest, ...She was basically surviving off ensure. Got to the point she was so weak and had to be hospitalized. once the had her hydrated n got her stabilized... Ran various test n an ultrasound revealed a tumor. 7 days later she had an operation to remove it.That was 7months ago. She is doing soooo much better. ...sorry for the long story but all I'm getting at is that it could be anything. Just make sure you explore all possibilities. At one point she was prescribed megace... An appetite stimulant. She never took it because she ended up hospitalized before we even got a chance to pickup the Rx. Good luck