You are not alone. What you describe is me to a T. My thoughts are so persistent, frequent and have been for so long that its almost as though I have learned to live with them regardless of how awful and clear. I've sat there listening to someone giving me really positive feedback, smiling and nodding and saying thankyou, whilst contemplating seriously specific and detailed thoughts.
I hope you are seeking and receiving help. Medication, therapy or a combination could provide a great deal of relief but it is a very different journey for each of us.
But just know that you're not alone and there are ways of moving through it.