I have been coughing the past 4 weeks. It was a dry cough the first two weeks. My doctor put me on an antibiotic for 7days, and a cough syrup. The syrup helps me to sleep better, and tames the cough; however, it leaves a bitter taste in my mouth. I have a bad taste in my mouth most of the time, and now coughing up white foamy stuff when I do cough. It has a salty taste to it. I have a metalic taste in my mouth continuously no matter what I eat or drink. What could causing this?