Are you a diabetic or at risk for it? I am and when my blood sugars are high you can feel drained and too tired to do anything although that is anything so a pregnancy symptom. Being thirsty with really no relief can also be a sign of diabetes...that is how I found out 7 years ago. I would talk to your Dr and see what he thinks...it might be nothing.
Oops title shud say thirsty not thirty :-D