In your case, this might actually be down to the ecig.
Most e-juices contain a mixture of PG (propylene glycerol) and VG (vegetable glycerol) and the higher percentage of PG in the mix, the more dehydrating the juice. Personally I use a 70/30 mix of PG/VG and get a pretty dry throat, though I think it's a worthwhile sacrifice for the flavour boost you get!
I won't bore you with the science but I hope that info helps! It's probably also worth testing your blood glucose levels to ensure you're not running too high.