I have zero medical expertise, but it sounds like this situation could be improved with software. Given a database that contains an exhaustive list of every illness and symptoms:

    illness      symptom     diagnosis_symptom_set
    -------      -------     ----------------------
    id           id          id
    name         name        symptom_id (FK->symptom.id)
                             illness_id (FK->illness.id)
             

    (Pseudo SQL)

    SELECT diagnosis.name as name 
    FROM diagnosis_symptom_set diagnosis_sympt
    JOIN illness diagnosis ON diagnosis_sympt.illness_id = diagnosis.id 
    WHERE symptom.name in (hives, chills, weight-loss, .....)

This will at least give a patient awareness of what has been tried/tested and what remains, possibly saving them months or years.