Chronic Cough - Neurogenic cough? Issue?

I have problem of chronic cough for past 12 years that begins mostly in winters or with any infection and lasts for 5-6 months The cough is severe enough to interrupt my day to day life. Different doctors have diagnosed it as Asthma/Bronchitis/Hyper-reactive airways etc. All tests - X ray, PFT, blood tests, PNS CT are normal. None of the medicines work be it inhalers or oral steroids or gastro medicines. Could be a Neurogenic/Neuropathic cough related to vagus nerve? Here are my symptoms: 1. Coughing all day long 2. No coughing when sleeping 3. Chest feels relaxed for few minutes after waking up. 4. No coughing when too engrossed in something 5. Sometime I spit out small quantity of saliva colored mucus from chest. 6. Takes lot of effort in coughing. 7. Coughing stops for a few mins if I feel something spicy. 8. Coughing increase considerably if I go out in open 9. Coughing is little better if I stay indoors in warm temp. Does any one have experience in treating this kind of issue?