I have had the heavy lung feeling from
vaping 100% vg, but only when I'm
vaping pretty heavy all day. I got some 20pg 80 vg liquid and I've felt fine since I switched. As far as shortness of breath, it existed for me when I started vaping after quitting cigs. But it's been a year and a half and I don't suffer any kind of shortness of breath anymore.
I hope your drs appointment goes good and you find the problem, also remember to drink plenty of water.