I have pretty much the same one. Not some cute movie-like stutter where you repeat a letter couple of times. It’s physical and sometimes even my neck and shoulders hurt from it. I can’t recommend any exercises or medication, but I can 100% say that finding the right people helps. You really need someone who would patiently listen to you when you need it and helping you in social situations when you are too tired to speak. A friend, a family member, just someone to help you. Try to reduce stress in your life as much as you can. I know that it’s hard especially as a teen because you don’t have much control over your life yet. But still, try getting enough sleep, try cutting out caffeinated drinks, less screen time before sleep, don’t catch up on any bad habits. If you improve your mental health and fortitude now it would help you in the future. It gets better, even if your speech doesn’t actually get better, your attitude would change. People that are worth of your time would always listen to you without interrupting. Make life easier for yourself, write notes for people on phone or in a scetchbook. Be prepared for interactions.