My Mother has had a severe cough, running nose and watering eyes ...

My Mother has had a severe cough, running nose and watering eyes for months. She has been constantly tired and unable to sleep.She has also been experiencing dizziness and back pain. After explaining this to my Uncle, he told me to check her medication. I believe the culprit is Lisinopril. What I don't understand is why with all the side effects this drug causes-Why-Why-Why didn't the doctor take my 84 year old Mother off this drug. Why, After she constantly complained to him he kept her on this drug.