PG is a humectant, which can make you hold water, also causing the water in your system to absorb into your organs, eg. lungs, ears, nose and throat. It can be harsh in high percentage mixes. Also, nicotine can add to the harsh feeling. Max VG can have a similar affect on the system however...so damned if you do, damned if you dont. lol. Try a few different mixes and keep record of how each mix ratio affects you. Drink lots of water when vaping and try to use a regulated device to see if it helps. If you are using a mechanical mod without a kick, you can be using over 100w to get that juice cooking, which can become harsh to the user, even causing a sensation where it seams to be getting hotter and harder to use. In really high watt set ups, the PG will actually get pretty hot and vape off really fast, hence people who use sub ohm and high watt mechanical mods are using more VG. It is a matter of taste, don't get discouraged. Keep track and if your chest continues to give you troubles, see your physician. Always drink water when vaping and always use proper equipment. I personally stay away from mech mods and sub ohm set ups, I also prefer to stay at 50/50 pg vg ratios with 6mg nic, since I vape all day long. Good luck and keep us updated how your journey goes with the juices your trying!