I've been taking trumpet lessons for around 5 months now and while I'm happy with the progress I've made, I seem to have a problem with endurance. I find that I can only play for 20-25 minutes at a time, sometimes less, before my chops give out. If time allows, I put the horn down for a few hours and try practicing again later on but this is frustrating to me. I'm sure that as time goes on and my muscles become more developed, I'll be able to last longer. Is it normal at this stage of the game to only last this long? I feel like I need trumpet Viagra or something. I've also been a woodwind player for most of my life and therefore am not used to a brass embouchure. Could this also be a factor?