What are you doing for your pup to get daily exercise? Who is letting him out during the day while you and your wife are at work? A daily walk around the block is good exercise for your 90 year old grandmother but it will not even put a dent in a growing retriever pup.
Do you hunt? Have you ever been to a training day with an HRC or gone to a field trial or hunt test? Sporting dogs have an enormous amount of energy, they are made to go hard for hours at a time and even at 13 weeks, your puppy needs aerobic exercise, something that gets his heart rate up. You are going to end up with some serious behavior problems with this dog if he does not get adequate exercise and playtime. It is very difficult to get a puppy that young hard, daily exercise if you don't have another young dog in the house for him to wrestle and romp with. He needs physical and mental stimulation and to be getting out in the world so he is socialized. Get a crate for your car and take him everywhere you go with you, any time you are out running errands he should go too. Every minute he is not alone and asleep in his crate is good for tiring him out. I can't emphasize enough how important it is for him to get out and meet new people and go different places every chance you get. Let him see kids playing at a playground or at a soccer field, take him out in front of a hardware store or grocery store and let people give him treats for sitting nicely. The more time you put into him now the more well adjusted he will be as he grows up. He is still a very young baby, he's only been way from his litter mates for 21 days and he needs you to teach him everything. Are you signed up for a basic puppy kindergarten or obedience class? It's a great experience for him and getting practice and assistance from experienced trainers will help you a bunch. No matter what you choose to do with your dog, he needs a nice solid obedience foundation to be a good family member or a welcome partner for a days hunt or whatever. Retriever puppies are very mouthy but I suspect the excessive biting is a result of a ton of pent up energy. Do you leave him with anything to chew in his crate? Frozen kong, or an antler? Chewing is a big outlet for energy. Don't let this go, you are missing out on important growth and learning time for him, he's a sponge right now and you don't want to miss out on teaching him everything you can.