Have you or your doctors considered SIBO? It stands for Small Intestinal Bacteria Overgrowth. It is diagnosed using the Hydrogen Breath Test and is treated with antibiotics. I lost 34 pounds over a period of 2-3 months. It started with food poisoning. Anyways, I had all of the same tests with all of the same results. Finally, I had the breath test which came back positive and am being treated with antibiotics. Not all of the symptoms are gone, but I definetly feel better than I did and my weight is currently stable. Look it up online and see if the symptoms sound familiar.
My weight fluctuates up and down quite rapidly all the time. I have Lupus, RSD, IBS, Acid Reflux and Thyroid disease. The Thyroid disease causes my weight to go up and down, but the other diseases make it all worse too.
I was 120 lbs and now I am down to 107 in a matter of a few weeks. I hope you can figure out what is causing all of your weight loss, it sucks being sick.