There is an easy and cheap test that is actually accurate. You place Petri dishes with a specific medium in them in the room, open, for an hour. Then you close them and put them in a dark spot for a week. When you next look at them, count the colonies that have formed. 3 or 4 or below is fine. 3 to 6 or 7 you need to wipe the walls with citrus oil cleaner or diluted bleach, deep clean carpets, remove old books and otherwise deep clean the space. More than that, you likely have mold issues in the walls or ceiling or floors. All mold issues come from water sources- small leaks in plumbing, old seals around the edges of bathtubs, ingress from clogged gutters backing up, etc. here’s where you can get the petri dishes- https://immunolytics.com/store/ Don’t bother with the kit or with paying them to interpret results, just count colonies like I outlined above.

We are going through this now. It’s no fun at all. We have the house ripped down to the studs. A couple times the plates saved us, showing there was more mold then we’d thought. We’d rip out some stuff we’d found, run the test, find too many colonies on the plate then dig some more only to find more issues. Finally, we are getting clear plates, and I feel much better.

If it does turn out to be mold and fatigue caused by the mold feel free to contact me as I have been through it and am now on the mend. It’s a long difficult process with only the vague signals you mentioned to guide you.