It is entirely possible to have Lupus and Fibromyalgia (I have both diseases). One should not be disregarded just because a person has the other. Yes, the symptoms are quite similar. The biggest difference being: Fibromyalgia is NOT a disease..it is a condition and it does not affect internal organs or joints. Lupus, on the other hand, IS a chronic disease which can affect your internal organs, cause inflammation throughout the body and is replete with relapse/remission.
It might behoove you to insist that your doctor continue to test you for Lupus if you feel that your symptoms cannot be attributed to Fibromyalgia. Here is a web site to help you distinguish between the two:
I wish you the very best!
Peace and Blessings