I am anxious about being responsible for him. Not that DC or DH can’t care for him but function of habit and my nature, I need to be in control. I need things to be in a certain way.
What is it about the puppy that you feel is not in your control? How do you need it to be - what exactly is it that the puppy is preventing?
I hope that doesn't sound aggressively direct? It's just that from your posts I get this overwhelming sense that you are anxious, but no real cause you ca pinpoint about what the puppy is doing to create this anxiety in you.
The anxiety manifests itself in me not being able to eat or sleep. I am up at night with knots in my tummy and headaches from this all. I am trying to break it down into compartments and work out what we can do. In short, I am not able to be in the now. I look at the pup and go did we make a mistake, should we give him up, then panic about how to go about the latter.
This does sound terrible. And I agree you need to address it. But I do wonder if the problem is more with your coping strategy for stress than it is for the puppy.
Your puppy is sweet natured, training well, you have tons of support from a trainer and dog walker and he'll start doggy daycare. He doesn't sound massively demanding - but perhaps you just haven't mentioned that?
The lack of being able to relax - why do you think this is? What was the difference when the puppy wasn't in the house - what did you do to relax then and why is the puppy being in the house preventing that? Are you worried he'll get hurt, or start to behave badly if you don't pay him enough attention? Does it feel like a burden only you are carrying - and is that a justified thing, do your DH and DC need to do more?
You just sound overwhelmingly focused on giving up the puppy rather than treating the root cause of the anxiety, which doesn't sound as if it stems from the puppy at all, but has been triggered by the puppy.