I would have to say that it was when I read Bernstein's book and acted on what I learned:
- starting on insulin (which, like you, I had to go in and demand; no one was offering it or suggesting it).
- switching to low carb.
Those two things together are the greatest game-changers I've ever experienced. Nothing else is even in the running.
Your experience with your dietitian is both instructive and common. Instructive, because it highlights once again the YDMV principle -- you need to do what works for you, not what someone else has memorized as a rote one-size-fits-all formula. You're the one who has to live with the results, not them. Common, because it's symptomatic of a general disconnect between us and them. Take a look at this link.