I used to always have cracks and sores in the corner of my mouth, and have now realised that since I got diagnosed with coeliac disease and went on a totally gluten free diet, I have just not had them at all. Coeliac is another autoimmune disorder, so I guess the sores could be to do with lupus, but then again coeliac is a really common thing that is totally underdiagnosed - incidence of 1 in 100 people, but less than one in eight of these gets diagnosed. If you have other coeliac symptoms (wheat intolerance) or symptoms that might related to untreated coeliac disease (dairy intolerance, persistently low iron, B12, folate levels) then it would be worth getting the blood screening tests for coeliac done.