I had the same problem and for years tried everything and was diagnosed with everything including tree pollen allergy, hay fever, dust, etc. etc. I had antihistamines until they caused problems with my liver, nose sprays, eye drops, antibiotics etc. etc.
Then I was referred to an Immunologist, apparently I had a low level of protective antibodies against ‘Haemophilus B’ Ii just copied that from her letter so don’t quiz me on it!) Apparently you are supposed to develop your own immunity by the time you are around five years old and I didn’t. These days kids are routinely vaccinated but when I was a lad they weren’t.
The result is that I can now breath through both nostrils – most of the time – for the first time in my life and I do feel somewhat better for it.
Though we also discovered I have a low level allergy to ‘perfumes’ which leave me with a constant low level allergic response, so I have cut perfumed products out of my life as much as possible.
My advice is to get yourself referred to an immunologist!