Your dog came home 3 days ago. The rescue described a calm, friendly, easy dog, and that is not the dog standing in your hallway.
Nothing has gone wrong. You are meeting an adolescent dog in the one situation that shows you least about them.
Why week 2 is harder than week 1
A kennel is a predictable place. The same sounds, the same hours, the same handling, in the same order.
Your house is new, and nothing in it predicts anything yet. A lot of the first few days is your dog watching and working out where things are.
Then the house stops being overwhelming, and your dog starts behaving like the adolescent they are. That is usually week 2, and it is progress rather than a problem arriving.
Around the onset of adolescence, dogs respond less to the cues of the person who raised them, and that responsiveness returns later in the stage. Your dog is somewhere in that window, and you are a stranger.
Lower what you are asking for
Decide now that nothing has to be trained this fortnight. Toilet trips, rest and a predictable day are the whole job.
Do not test what your dog knows. A sit, a recall or a stay in week 1 tells you nothing true about them.
Cancel what can wait: the dog park, the visitors, the long walk with a friend's dog, the groomer.
Say your dog's name and feed them for looking at you. That is enough training for a first week.
Shrink the house to one room
Pick one room you can sit in, with a gate or a door on it. Put the bed in a corner away from the front door.
Let your dog come out with you and go back there to sleep. A whole empty house is a lot of space to worry about.
Clip a light house line on while you are in the room, so you never have to grab at your dog to move them.
Keep the bowls, the water and the chew spot in the same places every day, so the map stops changing.
Routine before training
Behaviour change is built from management plus reinforcement together, and in a first fortnight almost all of it is management. What you are building is a day your dog can predict.
Walk, feed and settle at roughly the same times, 7 days a week. The weekend version should look like the weekday version.
Walk short, slow and somewhere dull, on a harness. Sniffing is the point here, and distance is not.
Protect 2 long blocks a day where nobody talks to your dog, calls them over or hands them a toy.
Feed your dog on a mat for lying down, in 2 minute sets, twice a day.
Relaxation is trained as a behaviour in its own right, in short repeatable sets below your dog's threshold. Start it in week 1, because most of the rest sits on top of it.
Alone time, from the first day
Gradual departure practice, short enough that your dog never starts to worry, is the core of alone-time work. A dog who arrived on Friday should not meet a 4 hour absence on Monday.
Leave the room for 10 seconds on day 1, and come back before your dog gets up. Repeat it often.
Build toward a few minutes across the fortnight, at your dog's pace rather than the calendar's.
Leave a chew down as you go out of the room, and let your dog finish it.
If your dog panics as you leave the room, stop adding time. That is a different piece of work, and not a first-fortnight job.
What is ordinary in the first fortnight
Toilet accidents in a house whose routine is 4 days old.
Broken sleep, pacing, and a dog who will not lie down while you are in the room.
Following you from room to room, including into the bathroom.
Hard mouthing, stolen socks, and a recall that does not exist yet.
Safety note
Book a routine veterinary check in the first fortnight and say your dog is newly adopted. Sudden behaviour change warrants a veterinary examination, and pain frequently presents as a change in behaviour rather than as obvious lameness. You have no history for this dog, so nothing has been ruled out yet.
Everything from here is reward-based, which is what the veterinary behaviour guidance recommends for training and behaviour change. A dog who has just changed homes is the last dog anyone should be correcting.
Safety note
Get help now if your dog growls, snaps, freezes over food or a bed, or is frightened of the people in the house. Do that in week 1 rather than waiting to see how it goes. Speak to your veterinarian and a qualified behaviour professional who uses reward-based methods, and tell the rescue.
Today's version, in one line: put the bed in a quiet corner, keep the day to one room, and ask your dog for nothing.