I start playing the first practice session of the day and I sound pretty good for the first few minutes. Tone is good and the notes are clean. But after just a few minutes everthing starts to go down hill. After 5 or 10 min I'm done and can't get anymore clean notes. If I rest for an hour and come back I can get another 5 or 10 of clean notes. So is this typical for a beginner of one month?