I think that its Diabetes Insipidus
because these were the symptoms I was going through when I was diagnosed with Central diabetes Insipidus 23 years ago.I know how you feel so please as soon as possible visit endocrinologist
because its a very rare condition and all doctors cant diagnose it.There is a test to confirm diagnosis of Diabetes Insipidus known as water restriction test in which you need to stay for a day or so in the hospital.
I hope it helps!! If you need more information you can always count on me.