Do be aware that this is normal puppy behavior and isn't likely to be a sign that he is becoming aggressive.
As suggested, when he takes your hand in his mouth, tell him no (not too loudly. As you've found, that adds to his excitement) and redirect him to something appropriate to chew on. When he bites hard enough to hurt, you need to let him know. Yelp loudly, immediately break eye contact, stand up and turn your back on him for 30 - 60 seconds. After that time, all is forgiven. In this way, you teach your pup what is called "bite inhibition".
Be sure you have lots of chew toys and bones for him to chew on. When he is chewing on something appropriate, PRAISE him heavily and drop a small treat. Always reinforce good behavior. Behavior that is rewarded increases in frequency.
Good luck! This too shall pass.
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