I went through this in my first trimester mainly. I did end up with GD, but don't think they are related. I think it may possibly be to do with your body making all that extra blood (I think it is 50% more than normal) and it needs water to do it. I don't know if that is really the reason, but that is my theory anyway.

Mine passed around 15 - 16 weeks I think. How far along are you?