Hi, you should talk to your teachers about it if you feel the work is too easy for you, as this could be holding you back or slowing you down.
As for grades needed, I'm sure you know otorhinolaryngology is a specialty within medicine and surgery, so you'll need a good range of GCSEs, A levels, and some accompanying aptitude/admission test scores too to put you in the best light. Not sure what year you're in now, but taking separate/triple sciences may be advantageous for when you study sciences at A level. Also, it's worth thinking about volunteering and work experience if you haven't already.