A Mild, Yet worsening Stutter (I'm only 15)

A Mild, Yet worsening Stutter (I'm only 15) When I was very young (~4) I had terrible speech. I stutter, talked too fast, and mispronounced most words. My parents got me speech therapy that got rid of my bad speech, and now I actually have a pretty posh voice. Unfortunately, I still have a mild stutter, although such that 90% of the time, I'm fine. However, recently (last 6+ months), my stutter has been getting worse. I've even found I stutter when talking to myself, almost more. I have a good amount of High School Exams, GCSE's (UK) coming up, I assume this is at least contributing. An ideas on why? And on how to improve my speech? Thanks for any replies.