4 pounds in two days probably isn't permanent weight loss, just fluctuation. Usually healthy weight loss is 1-2 pounds per week. I lost 5 or 10 pounds when I first had to go gluten free after my celiac diagnosis, because all I really knew what to cook was grilled chicken and veggies. Then I learned the ropes some more and went back to normal eating. However, gluten-free isn't a weight loss diet, it is a medically necessary diet to prevent exposure to something that makes you sick, just like a diabetic would be on a sugar free diet.
If you do end up being diagnosed as a Celiac and go gluten-free, you need to understand that any of the processed gluten-free foods are usually worse for you than non-gluten-free foods, like more calories, fat, and sugar. If you eat the unhealthy replacement foods, you will gain weight. Also, many people who are malnourished from advanced intestinal damage will gain weight once their intestines heal and they start absorbing again. However, the recommended starting point for a newly diagnosed celiac is to 1. Avoid eating out because you will get cross contaminated and that is not good for healing. 2. eat whole foods on the outside of the grocery store like meat, veggies, and fruit, and 3. Avoid dairy for the first three months.
If eating whole foods and getting your veggie intake is very different from what you currently eat, you may lose weight. Especially if you eat a lot of processed and prepared foods like I did and change your habits to the other end. But, if you end up re-learning food habits, you can use that chance to make your habits more weight healthy as well. Let us know how the GI appointment goes!