My black lab...?

Is driving me totally up the wall. He's 11 years old, and for the first 10 years of his life, he was a pretty independent animal. He still acts like he did when he was 3, and shows absolutely no signs of tiring out. But in the past few months, he's developed some strange habits that have me up from 3 to 5 am tending to his every whim. Every day at 2:30-3 am, he'll wake me up whining and barking to go outside. I let him out, and he walks to the end of the porch, sniffs around for a while, then returns to come back in. When I let him in the house, he insists on going downstairs (you need to wrap your arms around him and drag him into the rest of the house, which is separated by a swinging door), and I usually let him and go back to bed. Half an hour later, he's barking downstairs to go out again, where he repeats the sniffing air thing. When he comes in next, he consents to be let in the main house. This continues for the next two-three hours. What on earth is going on?