The ear anatomy explanation is great, thank you for that. But short and sweet and to the point correct answer is that nasal passages swelling or inflammation ( the other word for it) is mostly

Because of either cold, allergies, overworking Yourself, lack of sleep or all the above. To reduce swelling or inflammation in the nasal pharyngeal area you’d need nasal decongestants. He will most likely see immidate results with those including a reduced headache. But I still recommend going to get antibiotics if the pain is as bad as he is describing @jack