Is a heavy feeling in the lungs normal when you first start out vaping?
I had the same problem but I found it was the flavorings, not the VG bothering me.
Buy a small bottle of straight VG with no flavoring in it, just NIC and see how it effects you.
I'm now using 100% VG juices and found juices that are giving me no problems.
PG is too harsh for me and causes a sore throat.