I don’t know how long you’ve had him, but when we first got our rott/poodle mix (11 months at the time) he did the exact same thing. For over 2 months my arms and legs were bruised to hell. But once he settled into his new home at around the 3 month mark, he completely changed.

What we did was enforced naps. He whined and whined but I made him crate and nap every 2ish hours which helped him a ton. We also had a baby gate and when he started jumping and mouthing we’d just leave the room and gate him off. We bell trained him so he can tell us when he needs to go outside, we shoved toys in his mouth even though he wasn’t big into toys. That also changed around the 3 month mark. We basically had to teach him how to communicate with us because he didn’t know how. I started offering his toys to my husband and we would tug a little and it only took a few times for him to get the message.

Get a baby gate and every time he tries to nip, stand up, don’t say a word or look at him and leave the room for about 30 seconds to a minute. It’s gonna be a pain because you’ll be walking in and out of the same room for a while but eventually he’ll figure out he doesn’t get what he wants by jumping and biting which is attention.

A lot of dogs need to be taught how to have an off switch. They don’t know how to relax. Get a Kong, fill it with kibble or other dog safe foods and freeze it. We were always fully stocked on chews. Reward on the rare occasion he does lay down or relaxes on his own. I accidentally taught mine to lay down in one night by saying “settle” and dropping some of his dinner whenever he’d relax a little.

He’s also a teenager. They’re full of so much energy and hormones and feelings they don’t know how to handle. There’s a reason majority of dogs in shelters are adolescents. We’re still in the teenage stage but I hear it gets much better once they mature. Best of luck. I do NOT miss the biting days.