myrtle and cocoa helps. Just make sure it's actually young myrtle and mid-aged cocoa.
Do you have any allergies to pollen, etc? Sometimes these will cause the constant coughing.
It could be something called a GERD cough. Is the cough like a constant clearing of the throat?
GERD is heartburn and not all patients actually feel symptoms of heartburn but only suffer from this mysterious cough.
Because I am not a physician only a Medical Assistant I can give you treatment advice. However, try some OTC (over the counter) medications for heartburn for 2-3 weeks and see if that helps. Prior to trying anything always consult your physician to make sure that it is safe for you to take.