I would guess he is responding to a local female!!!!
My dog is exactly the same at the moment (all night!!). My boy is 13 now and has arthritis, but this afternoon dragged me at 90 miles an hour round the walk. I was up all last night with him, took him out and half an hour later had to take him out again as he was woofing loudly (next door have young children).
Nothing you can do to shut them up - afraid this over rules everything, just sit tight and it will eventually go away. When they get really crazy and howl at the door it is very nearly over (within a couple of days).
This is when it really annoys me that people take their female in-season dogs out last thing at night (like midnight) and then again first thing in the morning (like five/six). Maybe it does avoid male dogs on the street but when they walk past my house it takes me about 4 hours to calm my dog down and then they walk past again!!!! I get no sleep!!!!
They can also go off their food - so if he is not eating much don't worry.
Oh, and if he is young enough book him in for the snip it will cure any future problems!