you may just need to adjust to vaping. whether better for us or not, it's still a foreign substance newly introduced to our body that's not essential for survival. the body is bound to react. i had the same thing. had it again when i went from mouth to lung inhales as the back of the throat took a more direct hit. and again as i increased to 20 watts for more vapor.
as long as you're not getting burnt hits, just keep hydrated and take a break when you can. maybe keep some sore throat spray or lozenges on hand for especially irritating times.
another option is to consider a different juice, flavor or pg/vg ratio. one of those may be a major contributing factor as your body adjusts. even moreso, you may just be sensitive to one or more of the above.