Hello emma: I find myself doing a lot of this too. Sometimes I catch myself having conversations with myself, or with other people who aren't there, & I just shake my head & smile to myself at the thought of how hopeless a case I am...

You mentioned you practice meditation. But it's hard for you to do & it's not helping. I've also practiced meditation over the years. And I'd also have to say I never really felt as though I derived much benefit from it. It's kind-of a long story, & I won't go into the details here, but I recently switched from doing sitting meditation to doing a mindfulness yoga & exercise routine. (I also do some walking meditation.)

In my case, I'm an older person & I'm retired. Plus I lead a pretty-much thoroughly solitary lifestyle. So I have time available &, as a result, I spend a couple of hours a day at my practice. It's not a cure. But it really helps curb my generalized anxiety which I presume is at the root of much of my own self-talk. If you're interested in the practices of mindfulness yoga & walking meditation, one book you might take a look at would be Jon Kabat-Zinn's book Full Catastrophe Living. It details the stress reduction program that was (& presumably still is) offered at the University of Massachusetts Medical Center.

Also... I don't know if this will be of any help, but here's a link to a wikihow.com article on how to stop talking to yourself:

How to Stop Talking to Yourself: 11 Steps (with Pictures)