Yes it is normal that he sleeps alot. But wait, I've heard of 3 mo. old danes weighing over 60 pounds!
I have a five month old Dane and he is about 65 LBS. My Vet said you dont want them to grow to fast as long as there ribs arent sticking out and they dont look malnutritioned dont worry. She also said they grow in spurts.
check the puppy's food, XL breeds should not have a lot of protein as puppies. We feed our puppy Bil Jac large breed puppy food and is growing a t a great amount of speed.