I live in Poland and I also sing. I developed a cough in November which stayed for three months almost. It was cold outside, not good for healing the cough and staying indoors all the time also didn't help. I believe that your body needs to warm up and start it's natural healping process on the inside so it can go through the normal healthy way of clearing the cough itself. Why do I say this? Because I would cough everytime I started to sing a phrase and really, it was impossible to sing without that impending cough feeling in my throat and chest. It was just horrible and nightmarish. Until, I went to India for about 10 days. In India, with the warm weather, the cough disappeared on the first 2 days. The doctor who I saw said it was all in my mind because he saw nothing wrong with me, he ruled anything that could result in a cough. I suppose his reassurance that I am making the cough myself helped too. (Sometimes cough will stay because of being stressed, because you are constantly breathing high in your chest and this creates those conditions to feel like coughing.. and developes into a high-breath-cough cycle maybe? I'm totally shooting in the dark with this last bit but anyway...).