I don't know. I keep wondering if it's my imagination, but he just wants to go outside ALL the time. We will let him out, and within a half hour he's whining to go out again. Tuesday night he had an accident in the house. He's been house trained for over 1-1/2 years now, and he's not had a single accident since (till now!) AND....he had just been outside 1/2 hour earlier!
So I don't know what is going on with him, but I'm off today, and I figure I may as well take him in and get him checked out.