Hello, So I Have Some Concerns About My Weight. I

Hello, so I have some concerns about my weight. I am a 19, 5’10” male and I weigh 110 pounds. I have almost no fat on my body, although I do have some muscle. Obviously my metabolism is high, but why? I’m also very easily fatigued despite eating and drinking before and after physical activities. I would say I eat and drink a fair amount, although there are times where my body will reject food and it will be hard to eat normal portions without gagging. Am I iron deficient? Do I have a thyroid problem? Do I have an absorption problem? Thanks.