Nice that your doc leaves you hanging like that.
Low cortisol can be life threatening if you get sick - and if you have it, you will need to take steroids - corticosteroids - to support yourself so you will have an immune system back. So while you are fine (sort of) day to day, you need to make sure that you do not get ill, and if you do, make sure that you get to a doctor quickly.
I am also an endocrine and auto-immune nightmare, and my adrenals are gone - and for the doc to not test you immediately and then treat you is just plain, strange.
Get the following tests...
24 hour cortisol urine
Cortisol AM (before 9 am)
ACTH
Vitamin D
Complete immunoglobulin work up
Complete CBC with Differential
Blood chemistry (including T3 and T4)
Nothing can be diagnosed without a complete work up.
Cortisol levels change through out the day as we eat, drink, etc... an early AM cortisol is the only determination of where your adrenals are at in functioning.
Make certain you're seeing an "endocrinologist" and not a GP or Internist.
That's the best thing you can do at this point to iron out where your body stand healthwise. From there the test results should pinpoint which area(s) of your body are causing you the most issue. You might end up getting an MRI or CAT scan to see if you have a "mass" that needs to be removed.
Just my thoughts...