It turns out that my sister, who swore she would never try a gluten-free diet, is giving it a try. I don't know what all of her symptoms are, I just know she has not been feeling well and the doctors tell her she is just fine. She had a blood test for Celiac, some allergy, and her thyroid and all came up perfectly normal. They just assume that means there is nothing wrong but with the way she feels I'm sure she would tell you otherwise. I was looking up information on Celiac.com and found that a lot of people who are gluten-intolerant but don't have Celiac end up with negative blood tests. And my son also had a negative test result and he is extremely sensitive to it. So she has decided to try the gluten-free diet to see if it makes a difference. I hope she doesn't have it, but at the same time it would be a relief for her to find out what's wrong and be able to find a solution to it.
UPDATE: My sister has been feeling much better on a GF diet. She did a trial for a few weeks and then ate gluten again--not a good result. Of course, real results are complicated by the fact that she is in the first trimester of pregnancy so morning sickness doesn't really help. But she was convinced enough to avoid all her favorite foods. People just don't go on a GF diet because it's fun, you know? If you really do feel better it is worth it!