Vaping the same flavor for too long can make your taste buds get used to it and it tricks your brain into thinking there isn't any flavor. Allergies, colds, flu or any nasal problems can also mess up your sense of taste. Then there's the "flavor cycling" where your taste buds are going through a regeneration cycle, which can also mess up taste.
Try switching flavors, using mouthwash or eating some crusty bread to see if any of these help.
If your throat is sore or burning, drink more water. I cannot stress enough that both PG and VG are dehydrating. They're hygroscopic, so they attract water and this helps create the vapor you exhale. Drink water, drink water, drink water!