Hi! I'm 17 (F) too and I've been stuttering my whole life as well at least since first grade, which is the earliest I remember)! It's my first time commenting on this subreddit, but I can relate to your presentation anxiety as well. However, mine is with a one-minute presentation that's only worth 20 points, and I've spent more than a week rehearsing over and over again at this point. I actually find that for me, the facial feedback effect sort of works!! Whenever I smile more or think of good memories or people I love I typically end up doing better. Back then (actually not that long ago since I figured this out kind of recently), I ended up in a feedback loop where I would be anxious about stuttering, and then I would stutter, become upset, and then become more anxious, leading to worse stutters that kept going and couldn't stop. I don't know if this works for anyone else, but it definitely makes a difference when I'm in a good mood and think about all the good things in life!! I wish you all the best, and I believe in you.