You should get several sets of testing and
not just saliva, but blood as well (free cortisol
can sometimes have issues with cortisol
binding globulin if estrogen levels are high). You also need other tests like sodium and potassium (it is a salt wasting disease) and a stimulation test.
Hydrocortisone suppresses the adrenal gland, if the dose is high enough. A normal replacement dose varies from 10-30mg daily, divided up to mimic a normal diurnal rhythm.