Lupus is very hard to diagnosis and often part of the diagnostic process is to see how your symptoms react to certain lupus medications. Plaquenil will not harm you, and is almost always used as a first med for lupus and many other auto-immune diseases. It may take up to 3-4 months to observe any changes in symptoms - a few people have some stomach upset that goes away after a few days.
Does it sound like Lupus? Maybe, but could be lots of other things as well, thus the "undefined disease"...sure he didn't say UCTD (undefined connective tissue disease)? That is actually a medical diagnosis. I think you should follow his advice and take the medication he prescribed you...if you don't make sure to tell him.
Lynnwood, Lupus & Sjogren's ModeratorDIAGNOSING-LUPUS & LUPUS-RESOURCES
"Life is far too important to be taken seriously" - Oscar Wilde