Omg im In almost the exact same situation. Im 17 now, and I first noticed I started stuttering when I was maybe 14. It's so frustrating and I agree with everything you said, I get it mostly when I'm with family or close friends, when I try to start a sentence or ask a question, and it's not even there if I'm rlly mad and I can speak very fast. I have no idea why I have a stutter now, my mom even tells me "I wonder why you stutter, you never did when you were little" and it's so frustrating. Mine also is worse some weeks and better another week. It's all random. Lmk if you find a solution or something haha it makes me so mad at myself