I hope all goes well at the vets. I could have written your opening post, the constant standing up and down, the relentless nipping and wanting attention. The not being able to move because he would get up and follow me the minute I did so, even though he was napping. He has to go in his crate for naps if I am busy because he will still wake from a seemingly good nap if I so much as answer my phone.
I have / had very similar problems to you including food, with my springer puppy. He was in the vets at a few weeks old as he was very poorly and dehydrating with his diarrhoea and he has been on hypoallergenic food ever since, though it's both wet and kibble. So far any time we have tried to introduce a different food or treats he gets an upset stomach. He never has treats, we use the kibble for treats and training.
I work from home so I thought this would be ideal but his biting, snapping and jumping up drove me to tears, my clothes have holes in where his puppy teeth nipped or hung on. It was constant and at times I felt I was being attacked. Fortunately he's always been happy in his crate and so I used to put him in there for time out. I needed that time out too. My DH has come home to me in tears on more than one occasion.
Biting / Chewing
He is a chewer and no toy has lasted long no matter how tough, Nylabones were
useful when he was younger, bones like sweet potato or filled with peanut butter etc upset his stomach but he needs something in his mouth so he has olive or coffee wood sticks, a split antler, coconut rolls or filled bones, we scoop out the filling and put his food in. He loves and can tolerate Yakers sticks and when these get small they go in the microwave for 2 minutes and blow up into a cinder toffee type treat.
Whenever he started to nip or bite we swapped my hand, foot, ankle, insert body part here .... for a chew of some description.
Feeding is spread through the day ad hoc, so often when I need to be in a meeting or get on with something or distract him. We don't use a bowl we stuff a kong, we use varied lick mats and found a wobble kibble dispenser that he hasn't broken yet (he's broken two and he's only 6 months same with a puzzle feeder) We stuff bones with food, freeze carrots and a smaller kong and scatter feed with kibble which we also use for rewards.
Jumping / Mouthing
He also jumped up constantly and so we ignored him, turned our backs (it didn't stop him hence the holes in clothes) then we praised him giving him kibble when he had four paws on the floor and eventually his jumping became less. We also taught him to wait (with limited success so far). So now when we come home, or when he gets up in the morning or visitors come he is learning to sit before he is acknowledged. He is also getting very good at this out walking, he will sit while people pass including other dogs and if the person starts to talk to him I remind them he is a puppy and will jump up.
His mouthing is usually because he wants / needs something which he can't get to which could be food, his water or to be outside or he doesn't want you to stroke him etc. However it's also when he is over stimulated or excited and so he often needs some crate time, he may take a short while to settle if he's over stimulated but it works, he comes out calmer later.
Walking / Toilet outdoors / Exercise
At first he would not go for a walk, just lay down. A springer who wouldn't go for a walk?? Then he would only go out if I was there, we would have to carry him away from the house. Eventually my DH put him in the car and drove him half a mile away so he would go out with just him, and it worked. It took weeks for him to have a poo outside of the garden though and sometimes he would pull to go home just so he could poo in our garden. We praised him ridiculously when he did it elsewhere.
I can't take him out in the car though he will not settle for me.
He has regular crate time during the day even if we are at home doing nothing it helps regulate him. His exercise is either once or twice a day with me or DH, with me it is on a long lead in dog walk areas. With DH it is scent work off lead in the fields. Sometimes if he is out with DH for a longer spell we don't take him out the next day. We have a large secure garden and he goes out there but he has eaten quite a lot of it so its short supervised spells. We don't throw balls in the garden, scatter feeding tires him more.
So yeh he's like a toddler and having a puppy is a lot harder than I remember when I was younger. It has been so hard there are days when I dont even like him 😨
We haven't put a tree up that would be too much temptation and we would be constantly at him to get off it. He loves paper and cardboard and dangly things. He is faster than me and no he doesn't look like a cute Andrex puppy when he has dragged and chewed the loo roll across the room. Shoes are all on a high level, if it's within reach it's in his mouth.
Good luck, I feel your pain 🐾