I have the same problem. Did you find any answers?
If it's from a nerve, the area that is symptomatic will follow the path of the nerve, and since you don't mention that, it's probably not an inflamed nerve. It sounds more like a sinus problem than anything else. Have you tried taking a decongestant (something like pseudoephedrine or phenylephrine), to see if that helps? If it helps at all, that is evidence of sinus issues. I know you said you had a negative CT of the sinuses, but was the image taken when your symptoms were at their highest? When you have a problem that comes and goes, you may have to "catch" it with an exam when the symptoms are actually present. I doubt you are going to have to have another CT exam, since a chronic impaction should have shown up regardless, but I suggest making a list of what makes the problem better (even a little bit), what makes it worse (even a little bit), and any circumstances that seem to make the problem more or less likely to occur. Every time you have the symptom, write down you impressions of what is going on in your environment, your activities, your diet, and anything else you can think of that might be relevant. After a period of time doing this, you may get some clues. Good luck.