Hi there! Be honest with your Dr., tell him everything and remember, you do have a right to a second opinion. I am no dr and I do not know you but my opinion is, is that you need some cough medicine with some promethazine in it to slow down the cough and to keep you from getting nauseated, which is what the promethazine will help do for you. Sometimes you just have to stay on these dr's arse, if you know what I mean. Good luck and keep us posted on how you are doing. You might want to look up that medication and see if that is some of the side effects.
Hope you feel better fast. And also walmart and the other drug stores sells their brand of anti-nausea medication and you can always check with a pharmacist to see if they are alright to take together or if they have any suggestions, sometimes they know more than drs.