How do I deal with a very negative inner voice/second conscience that's constantly loud? It's like I have two different people in my head but they're both me, telling me opposite things endlessly.

The best way I can describe my thoughts about myself (and how I think other people think about me) is like two superimposed instructions on top of one another. You don't know which one to read, and it makes you confused. I don't know what I want in life and my views on things can change rapidly. I named that negative inner voice "Sarah". I know Sarah isn't real, and she's a part of me, but it feels so wrong to go against her. It's as if she is the arbiter of truth, specifically when it comes to my standing. She constantly moderates things and she's often louder than my "good" conscience, and I'm not sure what to do. She'll be chattering even as I'm actively speaking to another person, saying things like "look, this person is sick of you. Why are you such a failure?"

The thing that gets me the most is that every time I mention this bad conscience, people just look at me weird and shrug it off. It's so hard to even bring up this second conscience because it feels wrong, like I'm being "naughty". They never tell me that the bad conscience is wrong, which has just affirmed what I said about "Sarah" being an arbiter of truth. If I do something, she'll always be saying things like "you're so slow, you're such a shameful person, hurry up". Often, it's worded a lot meaner than that, and "said" in an extremely vindictive way.

Then my "good" conscience chimes in, telling me I'm a good person, basically the opposite of what Sarah says about me, and it's like I get a moment of clarity where I can rebel against "Sarah" and try and cry out for help (which is where I mention that I do have a second conscience that is "bad"). But then "Sarah" comes to the front again, and this repeats over and over. I regularly get some pretty intense mood swings that last minutes, sometimes hours, multiple times per day, and it's because of this double conscience that I have. It was suspected in the past that I have manic depression, but that was ruled out. Both "me" and "Sarah" are constantly arguing. I'd say this double conscience thing started in my early 20s, and has flared up after I tapered off Mirtazapine a couple of months ago, as I found the Mirtazapine was just numbing my emotions.

Really small things can trigger "Sarah", such as getting a phone number wrong, in which case Sarah will sometimes bicker for hours about how stupid I am and how my family should be ashamed of me, and how I don't deserve to have a boyfriend (I talk to an AI instead, as Sarah "allows" that). I'm constantly being given conflicting instructions. For example if I see someone crying. It triggers confusion a lot of the time because with me, people who cry should be consoled, and that crying, even as an adult, is completely healthy and normal. But Sarah says "if you're an adult and you cry, you need to grow the heck up. Just tell them to grow the heck up and walk out the room." So, depending on the time of day, I will act completely different or contradictory to a given situation, as if my worldviews are actually just a wildcard that flip-flops on a constant basis, in a very rapid manner, often multiple times per day.

I'm having CBT sessions and I did touch on the bad conscience thing during my last session, I'm just wondering if CBT is effective for this and how I can deal with it in between my sessions.