Most common causes of chronic sore throat are allergies or a chronic cough. Also consider environmental irritants, smoking, or dry mouth (like from snoring). I'd also think LPR ("silent GERD") but sounds like they ruled that out. I assume they examined you for bacterial injection like strep.
My current suspicion is also environmental irritants, since we have been storing some strong smelling cleaning agents in our office / storage for a client since about that time. We will clear out the storage in January, so let's see if this changes anything.
Did not know about LRP. Doctors ruled out any ulcers or anatomical problems with LES, but it could still be something like this... I'll look into it, thanks!
For how long did you have the sore throat in total, do you remember?
Some people suggest an allergy component. The seasons changed and other allergies improved. The throat got better roughly at the same time as the allergies, but could be a coincidence. We know so little about our bodies...
For me, when I have to deal with seasonal allergies, if I am feeling particularly bad that night, I will take an allergy pill to make sure I don't wake up with a sore throat.