i would try a different dentist, not only because s/he has not found a cause but also I think it remiss that you were not informed of simple hints like not rinsing your mouth with water after brushing, esp at night.
this has been standard advice for 20+ years.
I use colgate which has arginine in it, costs a bit more but seems to help. I only use it at night, to save it as I don't have much money, use a cheaper one in morning.
but do whatever helps you. try different toothpastes.
I used to use an American one based on baking soda which didn't have that extreme zingy shock, was a more gentle taste. arm and hammer. avoid charcoal ones, a con.
it's also good to minimise erosion not to brush teeth after eating for about 30 mins, esp if having sweet food/drink.
I think people were wrongly advised about this in the past.
the idea is to make one's teeth shiny clean before eating, so less adheres to them. then let saliva neutralise acids, before scrubbing the teeth with brush. best to just rinse with water or non-alcohol mouthwash after eating.
if problems persist could you go your GP, maybe ask refer to ENT. does the pain go up the side of your face, could be rheumatic ? neuralgia, or even GCA...
good luck.
these are just my thoughts. am not prof.