A few years ago I was tested for Vitamin D deficiency- probably for the first time. I came out at the low end of the normal range- which is probably normal in the Boston area, where I live. We don't get enough sunlight here for much of the year. My doctor prescribed a megadose of 10,000 units a day for 2 or 3 months and then retested. My levels were o.k. then, so she told me to take 1,000 units a day, which I do, in addition to the 400 units in my multivitamin.

My point is, maybe you need a higher dose- in addition to looking into the possibility that your really do have celiac disease, despite the negative test.