It could be Diabetes Insipidus caused by a problem with your pituitary gland which is not able to produce enough anti diuretic hormone leading to loss of urine and excessive thirst. I have had this myself for a very long time and I know that mine is caused by an infection in one small location of the digestive system. This triggers destruction of the pituitary and hypothalamus because of the effect on the vagus nerve. I have used Tu Si Zi (dodder seed) for a very long time to help control this because it increases the weight and function of the pituitary gland.
Do you have any other symptoms? Tiredness/fatigue?