From what I've read this is occuring because you're drinking more water on this diet, funny enough.

Your body is used to storing up so much water because of carbs and lack of water that when you go on this diet and start drinking alot of water you get your natural sense of thirst back.

You're body is thirsty more often now because you're not retaining as much water because it knows its getting water on a regular basis. Happened to me as well.

Hope it helped