
Hi! If you do a 'search' on this site (top right-hand corner of the screen) and type in "puppy biting", "pupy mouthing", "mad bitey puppy" or similar, you will find umpteen threads on the subject. It is a perfectly normal stage of puppy behaviour, and they need to be taught that we humans are silly delicate softies who can't play like dogs! It takes them time to learn this, and in the meantime it is best to keep a lid on play, and not let the pup become too excited.
Have you got a copy of "The Perfect Puppy" by Gwen Bailey? It is an excellent book which will answer this, and many other questions that you haven't yet thought of!