I had a kitten who did the same thing. He even sucked on my male dog! My vet said he may have been taken away too early, but he was 8 weeks old and eating solids so that wasn't it.
How long have you had the puppy? The separation from it's mother can be traumatic, and if he wasn't too young when he came home with you, then it may just be a fixation that will pass. You can try putting tobasco or bitter apple on your lab and that should deter the suckling, but try to deal with the underlying issue as well.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.