Not confident because you stutter? or you stutter because you're not confident?

Not confident because you stutter? or you stutter because you're not confident? I think it kinda goes both ways because when I just come back from the gym I feel confident and barely stutter or when I act a confident character like when I meet new people my age I try to act overly confident to the point where I stutter way less. On the other hand when I feel like my hair isn't good or I feel stupid I stutter way more since I'm focussing on the negatives that's why when I just stutter one time I feel like shit and I stutter more. My stutter is psychological so it can be a possibility, what do you do to get more confident while speaking and not avoid certain words?