You both mention self negative talk and for that reason I come forward with this recommendation, but things you discuss (repressed emotions, powerlessness/vulnerability, self-leadership,...) are all intertwined and addressed in the book in an insightful way.
The most important thing is to _experience_ Voice Dialogue (or IFS, which slightly differs in approach), ie. to be in the situation when someone talks to your 'voices'/'selves' and you 'enter' those 'voices'/'selves'. This experience results in a revelation which I tend to call (a deep) insight, no less.
VD precedes IFS (which is not that important) and I have a strong preference to VD over IFS (I would need to read more on IFS and clarify my points, which range from personal to very technical, to justify my preference).
You are on the right track. I'd speculate there are memories from your childhood that could be the root cause of it.
It will take time for things to change. To figure out what is going on and to listen to the messages from your body, but things will get better for you.
It took around 2 years for me (with reading and therapy) to make significant progress, but I had to exist in a world where some of the people who created the original issues were in my life still and were very unsupportive of my new revelations, which made the process harder than it needed to be. The process isn't over for me yet, but the hardest part is over with the PEM disappearing and depression abating.
Please drop me an email (email in profile) sometime, I'd be keen to know how you get on and what you learn.