From my experience the more anxious I am, be it for lack of confidence or fear of stuttering, the worse it gets. I haven't looked to much into possible other causes for stuttering, but from my own experience speech therapy is a far too easy trap to fall into. As I don't know what you've tried, what's been helpful to me is dealing with unresolved issues, unrealistic/unproportional thoughts, aka Cognitive Behavioral Therapy; but with an \*actually skilled\* therapist. I had once gone to a psychologist who, I found out later, didn't believe in evolution. Imagine that.