Diagnosing these auto-immune illnesses is quite tricky as the same disease will appear in 1000 different ways given 1000 different people.
Often how a patient responds to a specific course of treatment gives the Dr an immense amount of information that cannot be learned from tests. observations, or patient-reported symptoms. Don't despair! Treatment without firm diagnosis is very common and very necessary with auto-immune illnesses; not nearly as crazy as it sounds at first.
See the link below, diagnosing lupus, for the 11 symptoms, 4 of which are necessary for diagnosis. There is not one single definitive lupus test.
Hang in there,
Lynnwood, Lupus & Sjogren's Moderator, Dx: 2002DIAGNOSING LUPUS & LUPUS RESOURCES
"Life is far too important to be taken seriously." - Oscar Wilde