As mentioned above, puppies are usually high energy or don't like to feel "trapped" by cuddling. Give him time and let him do things on his terms. My boys prefer cuddling when they are tired after a big walk/outing/play session. They also cuddle and turn all lovey when they are trying to butter me up.
Try giving him a quick cuddle/hug and then let him go on his way. Sweet talk him. Try massage as Ann indicated to find what he likes, but don't trap him into it.
I'm convinced my boys became super affectionate because they know they are free to walk away when they choose.