Welcome to the forum, Anne.
Were you eating gluten when you had the tests? If you were avoiding it, that would skew the results. But endoscopy is the standard for celiac. Even if this is negative you can still have a sensitivity to just wheat or all gluten.
In addition to a gastroenterologist, I would see a good allergist. My very good allergist had me keep a good food journal to help us discover my food issues (sulfites). I'm back with her now, going gluten-free for a couple of weeks and then coming in to do "food challenge" with some whole wheat pitas. It's really hard to find pitas or any bread with no extra grains and also no sulfite preservatives.