I adopted a gorgeous 1 yr old boxer / pit mix recently. She is great indoors, house trained and mellow. Whoever owned before must have kept her in a box because she is a different dog outside. Everything stimulates her. She pulls on her leash and her walks are feeling like a chore. Additionally she cries when I leave my home. I feel trapped and regret her adoption. People are telling me things will change with obedience training, but right now I feel overwhelmed, my anxiety is sky high and I am struggling.
Hi. Welcome to the forum. Sorry it's under the circumstances.
First of all, it's normal. Everything you're feeling right now is normal. You're life has gone through a 180, routine has flown out of the window, and you're responsible for a sentient being who is her own personality.
Please speak to someone about your anxiety, but there are some calming techniques that you can do right now. Here's a couple - and I promise you, they work.
Breathe. In, 2, 3, 4. Hold, 2, 3, 4. Out, 2, 3, 4. Repeat as often as required. You will feel yourself starting to relax and your anxiety coming down.
The 5, 4, 3, 2, 1 method.
Name:
5 things you can see right now!
4 things you can hear right now
3 things you can touch right now
2 things you can smell right now
1 thing you can taste right now (if you can't smell or taste anything, imagine your favourites).
Colouring in/mindfulness/meditation
Now.
What you're feeling is so common it has a name - the Puppy/New Dog Blues. It will pass, once you get a routine in place.
When settling in, it's common for dogs to be anxious when their human leaves. Both of my girls had it. Her life have done a 180 just as much as yours has.

This is a great article on separation anxiety and has a game you can play to help her get over her anxiety:
Separation anxiety is something of a hot topic, something many trainers and behaviourists avoid like the plague and something widely misunderstood by the majority! So what IS it, and what ISN’T it. Separation Anxiety is used as an umbrella term to cover any anxiety based issues regarding...
www.thecanineconsultants.co.uk
As for leash walking, check out Kikopup (actually. Check out Kikopup for most things dog training

)
I would suggest watching a video on leash training, and one on crate training. Both are rather important for training in general, so always good to start with the fundamentals. Cesar Milan and Zac George both put out training videos on Youtube, as well and numerous others. They usually have a catalog of videos to make finding the right video in their collection for you to watch. On the walks, carry a bag of treats with you. Whenever the dog starts to pull, give him a command and reward him(sit, come, ect). YMMV.
Please do not watch Cesar Milan or listen to any of his advice.