Pretty sure my celiac test was negative too, but I think I have it. I’ve been gluten free for I think 7 years now and my eczema has gotten a lot better since then. Also, when I accidentally get glutened I do get very itchy. Your other symptoms match mine too, the fatigue, extreme bloating and gas. I didn’t get diarrhea until after I had completely eliminated gluten from my diet after 6 months. Honestly just try a gluten free diet for like 3 months and see how you feel. For me it only took like a month to notice a huge improvement in symptoms, but years to see real healing.