That happened to me when I started. Buy some eliquid with some VG in it. Try juices with 20-30% VG. Nicotine is a skin irritant. PG base lets through the most of nicotine's TH AND irritation and the most flavor. The vapor of medium or high nicotine in 100% PG can be irritating for the tongue and for some people's throat or lungs.
If you can't use different juice (like if Japan does not have PG/VG blends or if you are using prefilled cartomizers) then try one step lower nic. You won't suffer - just take extra drags occasionally and you will be getting the same amount of nic. Another option is buy similar juices or PG and Vg and blend them. A large bottle of PG eliquid and a small bottle of VG eliquid with a similar flavor and same nicotine and mix them - for example - a 30ml bottle of PG juice plus a 10ml bottle of VG juice = 75pg/25vg juice.
With stuffing-type cartomizers I also use a plastic or delrin drip so there is a larger hole delivering the vapor into my mouth instead on a thing stream aimed at my tongue. if you are using something 510-based I recommend Boge cartomizers (slim 510 needs the standard resistance ones, not LR)