Hi Cycleman and welcome to Psych Central!

Here are some links to negative self-talk that I hope can help provide you with some insight. Negative self-talk is largely habitual.

This Is What Negative Thinking Does to Your Brain and Body

Challenging Negative Self-Talk

Working with Your Inner Critic

Don't Let That Inner Critic Derail Your Goals! How to Grow Inner Resources for Change

And, when formed in childhood -- as mine was, so I am only speaking from my own experience with negative self-talk -- it's stored in the brain's amygdala and is controlled by the thalamus (not hypothalamus). Negative self-talk literally changes the chemistry of your entire body; effecting your cortisol levels, your adrenal levels...everything.

Negative self-talk is not just a psychosomatic "curable" symptom of depression. It's far more than just low-self esteem. It's a bad habit that was formed as a response to trauma or a psychologically toxic environment.

In essence, once that has formed, you're sort of stuck with it and the only thing you can do, is learn to manage it with different cognitive techniques. I've tried cognitive behavioral therapy, dialectical behavior therapy, nutrition (that's a HUGE one for me), breathing exercises, walking meditation, drumming, and writing and those methods seem to help me cope with my own negative-self-talk when it gets triggered. I "over think" things a lot, which is also a form of negative-self talk, because it's self-doubt disguised as over-analyzing or rumination or dwelling.

So, my take on negative self-talk's "cure" is that there is no cure. The only thing you can do, is figure out how to manage it.

Since you've seen professionals about it and they haven't helped, have you ever used nutrition (i.e. not eating processed foods of any kind, cutting back on sugar and junk food) to help you? I notice with certain foods, I get a "happy" feeling after I eat them; like with artichokes. I will literally feel giddy after I eat an artichoke. It's a nice feeling. I also notice, if I get enough sleep and if I take baths at night and follow certain routines, when my negative self-talk gets triggered I can address it better. I also use self-depricating humor when I experience negative self-talk. I try to replace it with something funny.

I don't know if my post helped at all. But my personal experience with negative self-talk is that once it gets formed, it is like invasion of the negative self-talk body snatchers in that it effects the body's physiology and the only way to handle it, is to use tools (nutrition, exercise, art, music, breathing, singing, etc. psychological tools like CBT or DBT). Maybe others have better advice for you. Anyway. Welcome to PC. It's a great place with lots of resources and a helpful community.