Update: First of all, I bought some pg nic (54mg). No smell and the issue has gone....almost!
The nic fixed half the problem. The smell and taste of the nic had completely gone. But that sharp sort of sting sensation I described remained! After an hour of experimenting I narrowed it down to the water I was using to dilute the vg. I bought some classikool deionised then distilled water at the same time I got the problem nic. This was what was causing the sharp/sting sensation.
PG nic/back to deionised water solved the problems.
Thanks for the replies everyone - helped narrow things down! Thought I was going a bit mad there for a while... almost like my brain was making it all up!