I was the same way with my first pregnancy. I could not get enough water and even with over a gallon a day i ended up getting dehidrated. Just make sure you are drinking water for your thirst.
I was reading recently about gestational diabetes signs excessive thirst is one of the big ones, so you may just want to be on the lookout for that, but it could just as well be your body telling you you need more water!
It's your body compensating for all the extra fluids it needs. Just keep drinking liquids and try to avoid too much sugar and salt, which distract your body from absorbing the fluid.
Me too im 17 wks now and still wake in the night with a really dry mouth x