I know someone who had a very rare disease that is very similar to lupus. Your mention of mouth sores made me think of it as the person had that as a early symptom.

Looks like they can mimic each other with a sharing of many symptoms.

adding the info if you want to read more about it.. probably not related.
Pemphigus vulgaris -
http://www.nlm.nih.gov/medlineplus/e...cle/000882.htm
more-
http://www.google.com/#hl=en&source=...443ffcb5a5cce1