I hope you said yes, and took the appointment anyway,
even though that is very disappointing, especially once you'd finally made that confusing decision and taken that action on it!
In the meantime, could you use the time between now and then, to get a dentist's opinions or some actual dental work, to clear up some of those possible additionally confusing factors?
(Partly so the neuro doesn't say; See a dentist and then, if you still have the problem, come back.

)
And it might also, in the meantime, be worth re-trying one script of that amoxicillin, just in case, it might help this time even though it didn't the previous time you tried it long ago. Any possible infection that it might address, would be making the pain worse, even if it isn't the only factor. I would think most any doctor would let you try one week of that, for sinus or other, I would guess.
These are just my thoughts. Of course I don't know what's best for you!
Part of my thinking is that any of those might help lower the pain,
and in addition, would be doubly valuable, because:
whether it did or not, knowing those results beforehand, might help you to get the most out of the neuro appointment, to have investigated those with those specialists, so the neuro will be more apt to give a better and clearer view.?