My saliva testing prompted my functional doctor (who also has an MD btw) to send me to an allergist for verification because the top of the cortisol arc was lower than they liked. This was me, including a great many vitamin supplements - in the beginning. The supplements came down over the course of months, or were altered one set for another, by both doctors in concert. I took my visit information back and forth between them so all three of us stayed on the same page.
It will definitely be good for OP to go to an allergist, because second opinions are a good thing and because the allergist is a specialist and may be able to make suggestions and tweaks. Mine did.
But don't get the OP freaked about supplements. Being wary is good, but use of supplements is not necessarily a red flag. Some of us have bigtime deficiencies that need correcting.
And although 'adrenal fatigue' isn't a thing, most of us laymen use the term because we don't know any better. As you mentioned, backed by testing, 'adrenal insufficiency' is definitely a real thing. And it is f%king miserable and takes a veeery long time to get over.
When the allergist/internist MD who consulted took one look at the 'spit panel' I brought with me from the functional doctor, they did the blood test. And when the labs came back, they told me I was dancing on the edge of a pit (correct me if I'm wrong, but I believe 'adrenal crisis' is the medical term).
What those two doctors did got me back from the edge. And yes, it involved a lot of supplements. And hormones and phosphatidylserine and a bunch of other stuff. And more dietary changes, oh joy. And major rest, whether I liked it or not, which also sucked, because life in the US kinda requires the work treadmill. But I did what I was told and was lucky enough to have some support from family.
But any time I called it 'adrenal fatigue' both doctors would pounce and say 'adrenal insufficiency!' Doctors really hate the 'adrenal fatigue' phrase. I guess the snake oil purveyors got hold of it first, which is why everyone gets their hackles up.
And that spit test (the one that is taken multiple times over the course of one day and gets frozen before being sent to the lab) shows the variation over the day of multiple hormones. It was useful to the functional doctor to help adjust my hormones since I multiple hormone issues incl. thyroid. Hormones are a balancing act, the precursors and the sex hormones affect the thyroid and vice versa, and cortisol is also a hormone, one among the many. The allergist and functional medicine doctor were aware of each other the whole time, so they could coordinate.
Since I came out the other side after about a year, I count myself very lucky to have had their expertise. Sorry for the novel, but maybe it will help OP.
/u/collectedd you seem to think all functional med doctors are borderline frauds, I'm sorry you've had that experience. The ones I've seen have all been MDs with the extra functional cert on top. YMMV, I guess. I do remember at one point in time chiropractors had gotten into the same situation - some people were using the title to try to tell people that manipulation - perfectly valid for things like frozen shoulder, etc. - could cure cancer. Ugh. Hopefully, predatory people using the functional title will get forced out. I could wish the same for all the jackoff doctors who dismissed my complaints and didn't discover I had celiac for damn near 30 years.
OP, good luck at the allergist!
[TL/DR; spit test, depending on type, isn't always useless, some doctors can get good info off of it. Taking many supplements, for a short time (several months) is not necessarily a bad thing. Some functional doctors have MDs (the functional appellation is a cert that they add with another two years of school.) The word 'adrenal fatigue' is a layperson term doctors really don't like, but the word the normal person might be looking for is 'adrenal insufficiency.'