I'm vaping at 18mg. as a pack a day smoker, this is what the store assistants suggested. And the juice is in store made. Do you think that might be the issue?
I vape stuff from 12-18mg, depending on the flavor.
Give them a call and ask what the PG/VG ratio in that juice is. If they're good folks, they should tell you. If it's high PG, (say, 60-40 or 70-30), then see if you can get some made with a higher VG content.
And also check out that link above. How you draw and inhale can make all the difference in the world when it comes to flavor, enjoyment and nicotine delivery.
As a minor nit, I disagree that PG "causes" throat hit. In 99% of our liquids, it's the nic in the juice that packs the wallop. PG is a thinner, less sweet liquid and lets more of it be felt. VG is a thicker, sweeter liquid and tends to mask it more. I really like high VG juices with high nic content and the right draw on my device.