The most likely explanation for your symptoms is allergic rhinitis, more commonly known as hayfever. Allergic rhinitis is often seasonal but can also last throughout the whole year, especially when it develops in adulthood. Common symptoms include sneezing, itchy eyes and nose, runny nose as well as blocked nose and sinuses leading to a post nasal drip.
Saline drops and Texa10 are not effective in the management of nasal congestion related to allergic rhinitis. The purpose of saline drops is to moisten the nasal mucous membranes, so that mucous is able to run out rather than blocking the sinuses; however this doesn’t help to decrease mucous production or prevent post nasal drip. Texa10 is a non sedating antihistamine. Oral antihistamines effectively decrease itchy eyes or nose and sneezing, however they do not prevent or improve nasal congestion.
The reason that you get some temporary relief from the Coryx is that it contains pseudoephedrine which decongests the nasal mucous membranes and sinuses. However this is a temporary fix, rather than preventing the problem.
The best medical management for allergic rhinitis is to relieve and prevent the nasal/sinus congestion with a nasal corticosteroid spray (requires a prescription). This would prevent the mucous membranes from swelling and decrease the mucous production, so that the post nasal drip will improve. The one that I recommend is Flixonase which you would use once daily. The corticosteroids in the spray are poorly absorbed from the nasal mucous membranes so it has a minimal effect on the rest of the body.
As the main cause of the hayfever is exposure to allergens, it is useful to have an allergy test to work out what you are allergic to so that you can reduce your exposure. Common allergens include house dust, pollen and animal fur, so it is essential to vacuum carpets regularly especially if you have pets.
The accumulation of mucous in the sinuses and the throat especially while sleeping predisposes to infection. Taking Vitamin C will help to boost your immune system so that you are less likely to develop infections. It is also important to avoid dairy products especially before bed as dairy increases mucous production.
Allergic rhinitis is the most common however, there are other forms of rhinitis (which just means inflammation of the nasal mucous membranes) including non allergic rhinitis or vasomotor rhinitis, as well as other conditions which cause similar symptoms.
I think that the corticosteroid nasal spray would do the trick, however I would recommend consulting an ENT specialist so that he can take a more specific history and examination to confirm the diagnosis, do allergy testing if necessary and then give you a prescription for the medication that you need.
Dr Gabriell Prinsloo