Hello! I am a beginner oboist and I can't seem to play E5 up to A5 clearly. When I play those notes, especially A5, there is a fuzzy sound. The sound is not clear. When I play B5 to D6, it sounded clear and better than E5 to A5. Is it because of my embouchure or the instrument? Thank you!

The only thing I can think of is that your thumb octave vent is dirty, plugged, or has water in it. Best to take the instrument to a qualified oboe repair tech for evaluation.