Yeah, I really find Days 4-6, after withdrawal but before week one is in the bag, to be very tough and I have lots of doubts.
I don't know any way to build resiliency except by challenging your edge--sort of like yoga. You take the stretch as deep as you can, to discomfort on the edge of pain and just hold it there for awhile.
It isn't fun, and in fact can be extremely uncomfortable while you are doing it. A yoga teacher told me once that going to our edges regularly made more space for us to Be. It allowed expansion--more freedom of movement of body and hence mind.
Maybe try a little yoga. I find it to be an increasingly critical tool in my recovery toolbox. I recently found a groovy podcast that you can also watch as video from a source called yogadownload. Various teachers and topics offering 20 minute sessions
There is lots of free content:
https://www.yogadownload.com/
You might try it as a starting point for engaging the hard stuff you are facing.
Some gentle practices, and maybe Yin Yoga in particular would help give you the literal metaphor of edge. It also just feels good to be inside you body and in the moment for a bit.
Plenty of room for tears in Presence--