Please may I ask if you’ve checked out with a doctor to see if there are any physical or emotional causes for this. It’s a bit more than most of us experience. The voices yelling at you for days for having sinned, particularly, isn’t usual.
Do you confess when it’s serious, and forgive yourself once you accepted that you’re sorry you’ve done wrong? But ist isn’t usual to berate ourselves like that, not for long anyway. It’s possible you’re overly scrupulous? As others sometimes do, I confess to sometimes saying to myself when I’ve messed up, “I’m stupid. I’m horrible” which I shouldn’t say anyway and it’s unhealthy to do so, but it isn’t out of my control.
Conscience isn’t a voice in our heads, not in the sense you seem to describe it, it’s realization that one has sinned, and regret, and asking pardon, and then we accept pardon (unless scrupulous).