My 4 year old whippet has got a soft cough and reverse sneezing. Also has green mucus from 1 nostril only and gags/wretches like trying to clear something from his throat. Tried 2 types antibiotics, steroids and lung worm powder. All tests so far coming back negative. Would love to hear from any one with any experience of this, and any ideas about what it could be and what remedies to try.