Have you tried professional speech therapy? You know that you can be fluent. That's a great starting position. See a speech pathologist. Let them do an assessment. It could be a very short journey to improve your sphere of fluency. You might need to see a psychologist / 'regular' therapist (IDK what the clinical term for a general therapist is.) Maybe there is a pill that will help. But I would encourage you to get assessed by a professional before self-medicating.