Hi thanks for contacting HCM.... Noted you have persistent cough and many test are normal... Organic cause seems less likely.... Cough here might by chronic irritation... Avoid smoking if have habit.... Rule out acid reflux disease as it can lead cough. Pentoprazole taken for it.... If chest discomfort feels bronchitis or asthma ruled out by pulmonary function test... You might have allergic cough.... Try to avoid allergen that lead cough. Levocetrizine useful. Ginger, onion , garlic are good for respi tract. Finally if it troublesome cough take codein or dextromethorphan... Dr.Parth