If you were a smoker before vaping I would find it hard to think that is what is causing it. Personally I was sick quite often when I smoked cigarettes, but have not gotten sick since switching to Ecigs. Since analogs lower the immune system, but according to a studies PG actually helps prevent illnesses effecting the respiratory system. Many people do report some respiratory issues when quitting analog cigarettes for a short time due to the detoxification process of the body, and the change to the intake of the carcinogens and with drawl. If it is anyway caused by ecigs the only possible thing I could think of is an intolerance to either the PG, VG. or flavorings being used.