What Causes Chronic Nasal Blockage And Drip?

My name is Phil. I have had this condition for over a year and have been unable to get a proper diagnosis. I have seen an alergist, my general practitioner, a pulmonary doctor and an ears, nose & throat doctor. I have nasal stuffiness, constant drainage into my throat which makes me gag and spit (discharge is 95% white - not green). Ocassionaly I will feel like I have a low grade fever, clammy and on a few occasions I have become disoriented. I have been prescibed different antibiotics, nasal sprays, steroids and enhalers. Nothing has helped up to this point. I m not sure if taking benadryl tabs even help anymore. No one has any answers as to what the problem is. I am very frustrated, please help.