Even if your blood test for Sjorgens is negative, celiac disease itself can cause dry lips.
"Since Crohns disease is the inflammation of the Gastrointestinal (GI) tract, located from the mouth to the anus; dry lips can often occur while having it. The inflammation in the GI tract creates pain throughout the body, which in turn lowers your nutrient intake. This lowers your body’s ability to nourish your lips, which in turn dries them out.
Celiac Disease is an autoimmune disorder of the small intestine, which the symptoms can include anemia and fatigue. Vitamin deficiencies often occurs in people with the disease, which comes from the reduced ability of the small intestine to properly absorb nutrients. The body therefore fights to nourish the body as much as it can but often doesn’t give the right nutrients to the lips, which cause them to dry and crack."
It can take years to heal or improve from celiac disease if you've been undiagnosed for a long time.
Accutane also causes dry lips as well intestinal damage or malabsorption problems.