I don't recall it ever being mentioned on this forum. I looked it up quickly and it said about
1/3rd of the cases are due to some underlying illness...which in it's may or may not be auto-immune.
Unless you see a rheumy and have an autoimmune disease diagnosed, or have other symptoms as explained here:
www.lupus.org I would doubt the existence of an underlying illness.
However, if the Drs treatment doesn't improve it in a reasonable time, I'd suggest following up with a rheumotologist -- they are the specialists in auto-immune diseases.