I have been playing the trumpet from 10 years now and have been practising for about 2 hours a day for the last 3 months. I always begin with a 10-15 minute warm up and usually will rest for the same amount of time before starting any pieces. My warm up consists of long tones, lots of lip slurs, scales and tonguing. I always find that even though I have warmed up, I struggle to play a piece through more that once without tiring and needing to stop for a while. When I have lessons I find that I am able to play for longer. Am I doing something wrong when I practise and how can I improve this?