> eating significantly less than everyone

I wouldn't focus on that, food intake relative to others will be misleading.

Have you tried a food journal? For a week, take a picture of __everything__ you eat or drink. Go back and review it at the end of the week, a month would be better.

If you review it and think "yes, this is a reasonable amount of food" you now have a months worth of data to shop around to a doctor who can help you. If you have the opposite reaction, now you have a baseline to work against.

As an aside, do you drink a lot of soda?