Hi Mac, It could be a number of things but the easiest is not enough activity during the day. Try taking him our for a walk at night, maybe throw around a Frisbee. Dogs are like children, they sleep better when they are active during the waking hours. Baring any medical issues he may just be high energy that keeps him from settling at night. Be sure to provide him with a comfortable place to sleep, our clients swear by a good dog bed.
If all else fails we have tried the Nutri-vet Pet-Ease calming dog treats. They are natural with ingredients like Chamomile, Hops, Ginger, Tryptophan and Taurine.