Dry mouth, eyes and everywhere etc. happens at least once a month if not 2 or 3 times. bloods neg for rheumy tests so is it sero neg sjorgen or hormon?

Possible: Sounds like you have done your research. Defintiely possible, consider seeing a rheumatologist to go over your symptoms.

Vague: Could be hormones, could be allergic reactions, could be some sort of reaction to something that meds, supplements, environment, hard to say. I would keep a journal and note when this happens, and write sown all your activities, diet, etc from that day and day before