same thing happened to me with out switching vg/pg levels...
vaped for just about a year on 50/50 & 60/40 (Vg/Pg) and all of a sudden as if someone flipped a switch, I could not take to PG. Sore throat, tight chest, hack up a lung every time I took a normal to long hit. Changed atty, changed tank, changed flavor... nothing worked...
I actually quit vaping for about 6 months because of it... When I started up again, the same issues happened. it was not until I pushed the Vg up to 80% did I get relief from the describe issues above. Now, I try to keep the VG up to 90% if possible and have no issues. In fact, now I subohm and produce a ton more cloud. If I dropped the Vg level back to 60% on the setup I have now, I am certain I would break my back coughing so hard... lol
my advise... go high Vg and add flavor shoot as needed... change tanks/set up to allow for the thicker juice if needed...