It could be any of the ingredients, or simple dehydration. Try switching flavors, brands, go 100% VG, drink lots more water.
Lots of people tend to jump on PG at first, but it could be any of them, or even the quality of your juice. Or something unrelated entirely. Try a proccess of elimination.
But yes, in my experience, citrus flavors can tend to be irritants if they're using extracts in their juice. If you can find a juice company that gets their flavors from base ingredients, that could also help.
Happy vaping.