There are many different conditions that are associated with both fatigue and thirst. All of them are conditions that should be looked into right away. You mentioned one of the most common causes of this problem, diabetes. Diabetes causes blood sugar levels to be too high. Subsequently the sugar in your blood spills into your urine cause you to lose more water. When you lose more water, you become thirsty and drink more. In addition, having diabetes changes your metabolism and can make you feel very fatigued. If you were my patient, I would check you for diabetes by measuring your hemoglobin a1c. This is the current test of choice to screen someone for diabetes.
There are other abnormalities that can cause someone to be fatigued and thirsty. Another condition is diabetes insipidus (not the same as sugar diabetes). High calcium in the blood can make you very thirsty and tired. All of these problems can be investigated by a simple blood tests.
I suggest that you schedule an appointment with your primary care physician
. He or she can take a more detailed history of your symptoms, perform a thorough physical exam, and obtain the above blood tests I mentioned. Your doctor
may also test your thyroid function and your adrenal gland function to make sure these are operating well. Good luck.