Sorry to hear that. I'd want a CT scan perhaps or at the least a referral to a specialist such as ENT surgeon who might be able to take this further?
I'm no medical man and I try never to use Dr Google but it sounds as though your GP has reached the end of his knowledge level. My view is that if your GP cannot solve the problem he has a duty to pass you on to a specialist. If your GP can't think of what sort of specialist you might need, then you'll have to brief the quack. My opinion of British diagnostics is that they do not merit first world consideration. This is due to national health financial constraints, and the quality of many GPs, not to the actual research capabilities of British chemists who are world class. Their efforts to cure human misery have now been seriously curtailed by the likes of Peta who have threatened air lines and shipping companies that disaster will befall them if they transport animals for medical research. So next time you pass a Peta petitioner in the street, blow him a little bubonic plague please!