Because Lupus is often considered a diagnosis of exclusion, we are often treated long before we are diagnosed. Consequently, I consider treatment much more important than diagnosis.
The fact that you are responding to prednisone pretty much points to Lupus and rules out Fibro. Fibro historically does NOT respond to prednisone, while Lupus does.
Also I've never heard of Fibro reacting to the sun, but it is a typical response with Lupus.
You might want to check with www.lupus.org
and find the local chapter. Then talk with them and see what local rheumies are active on the local board -- these are the ones with more experience and interest in Lupus, and generally are better matches for us.