Phone the vet first thing in the morning for an appt for a blood work up. They may want to do a urinalysis as well.

There really isn't any point in "guessing," as you will only worry. The best thing is to act, and find the cause.

If it IS diabetes, there are several people on here working with that, and I am sure they can provide guidance and support. But first things first.

Let us know what the diagnosis is!