It sounds like your mucous membranes in your nose are intermittently swollen. This is not just because you feel like one side of your nose is clogged, but because the side that gets clogged changes from one to the other. If your nostrils are usually clogged on one side, you may also have a deviated septum. The vast majority of the time when you have nostril swelling it is caused by some sort of allergy. In your case the allergy may be very mild with no other symptoms. If this is the case, then you may not have any other symptoms that would tell you that you have allergies. Your allergies could be something as simple as dust mites. These could cause a low level of swelling in your nostrils throughout the year. An upper respiratory tract infection which can also cause nostril swelling is less likely in your case because it your symptoms are going on all the time.
The best next step for you is to schedule an appointment with your primary care physician
. If your doctor
agrees that a small allergic reaction is what is causing your symptoms, then he or she may prescribe you a steroid nasal spray which may relieve your swelling.