Suggest Medication For Persistent Allergic Dry Coughs

Two months ago I dug a small koi pond. The weather was very hot. I developed a cough and could not say two words without coughing. I went to the doctors right away and she said she thought it was allergies. Treated as such. two weeks later it was not gone so she treated with zpac. Three weeks later I still have the tickle in the top of my throat and that makes me cough. I just had chest xrays and she said it is clear and wants me to come back in and she will try more asthma medications. I have never smoked or have never had asthma in the past.