What vg/pg ratio were you vaping from when you started until the cough appeared? The problem really could be a number of things,for me it was 100% vg juice, but it also came along with shortness of breath and a heavy lung feeling , so to speak. I just mention it because the problem didn't start up right away when I started to use the vg liquids, it took about a week til i had problems, and it didn't go away until about a week and a half after I went back to pg dominant liquids. This may not be your issue, but just thought I'd mention it as the issue may not go away right when you switch pg/vg ratios, if that's the problem.