Persistent cough before and during chemo...please help

Hello, in 2014 I was diagnosed with breast cancer hr neg. I would cough none stop hence I learned through a CT scan that my cancer has spread from my right breast to my lungs. I was first prescribed taxotere and herceptin. I did fine after the first cycle my cough went away. My tumors shrunk. After the 3rd cycle my breast was clean and the rumor on my lungs was had shrunk to 3mm. I was feeling great. My doctor kept me on herceptin which didn't do much good. Then shifter to a target chemo with xeloda and tykerb which were more of a damage than help. My tumors started growing fast up to 2.5cm then 3cm. I'm now on kadcyla my cough is back nothing is helping. This is my second course of kadcyla I still have another after which I will have to do another CT scan. I took antibiotics for my cough and many other pills nothing helps. My doctor is not of a help at all I feel like a lab rat.