1) there is ~ a 20% false negative rate on celiac testing.
2) they might not have run all tests
3) You can convert to positive at any time, it is something you are born with
the propensity towards, not the disease itself (usually)
4) Get copies of all lab work (not just celiac) and keep track of trends
if there is something on your celiac blood work that confuses you post
it here in the celiac/gluten sensitivty forum, and the gluten sensitivy is
something that would not show up in celiac blood work.

good luck