Yes, My Mother Is 89, She Has A Cough And

Yes, my mother is 89, she has a cough and can not get rid of it. I have taken her to ENT, primary care dr. This has been over a 5 year period, ENT gave nose drops and antibiotic, it stops for a week or two then returns. She said it does not hurt, nothing hurts, but some times when she coughs she has trouble catching her breathe. any suggestions are appreciated.
Beth