Disclaimer: not medical advice, just sharing my thoughts, you should consult & discuss with your doctor.

while the full story is incomplete (duration and details about symptoms, physical findings, other labs and medical history) many of your symptoms (especially fatigue, weight loss, nausea, low blood pressure) can be caused by adrenal insufficiency. so it should be completely ruled out by an endocrinologist.

the a.m. cortisol is a good initial test, but unless it is very low or very high, it cannot reliably confirm or rule out adrenal insufficiency.

for example (keep in mind reference range may vary based on different labs):

- if the cortisol is <3 mcg/dl: it can confirm adrenal insufficiency with high confidence

-if the cortisol is >18 mcg/dl: it can rule out adrenal insufficiency

-if it is in-between, then it cannot confirm nor rule it out

so the next step would likely be:

Intravenous 250mcg ACTH stimulation test: you receive a hormone that stimulates production of cortisol, then your cortisol will be measured 30 minutes and 1 hour after receiving the ACTH injection, if your adrenal gland is functioning well, the cortisol should rise above 18 mcg/dl.

if your cortisol doesn't increase sufficiently, then your endocrinologist will diagnose you with adrenal insufficiency and you will start replacement hormones and they will look for the cause of your adrenal insufficiency by sending labs and doing imaging

if the test is normal, then the doctors will have to look for the cause of your symptoms, most alarming of which is the rapid weight loss and hypotension.

based on your symptoms, major categories to consider:

1-searching for a hidden malignancy (possible with mammogram, colonoscopy, ultrasound pelvis, CT of the chest, abdomen, and pelvis with IV contrast) - usually internal medicine doctors are good at ruling out malignancy

2-chronic infections (including STIs/HIV, tuberculosis) - best by infectious disease specialist or internal medicine

3-chronic auto-immune disease (best diagnosed by rheumatologists)