My stutter appeared when I hit my adolescent years and gradually got better around age 19-20. I think you may be right that your anxiety and tiredness are affecting your speech. I know that the general anxiety of being a teen affected me, and as I got older and outgrew teenaged angst, it got better. It’s easy for me to say don’t be anxious about something that rightly causes you anxiety. You get caught in a loop about being anxious about stuttering and that anxiety causes the stuttering. If it’s an option, I’d recommend some speech therapy and learn some tools to ease the stuttering. Just knowing that you have some speech therapy to lean on if you need to might lower your anxiety. Following this sub and hearing other people’s stories and speech techniques could be beneficial, it has been for me. Know that you are not alone!