First off, I've been playing trumpet 5 years going on my 6th soon, and I have been having trouble lately with again, what I think is air. Any note after a G on staff, except an A or B flat on good days, I struggle to play. When I go higher my volume drops significantly, it's like when I go higher te volume switch goes from 100 full/loud sons to 40 thin/screeching sound. I do not know what the problem is. I also have a HIGH tendency to "grunt" while playing an A or anything above, which after a while of "grunting" while playing an A or above I begin to "grunt" playing an F on top staff line. I notice that I begin to tense my throat while I'm playing a G on staff or higher. My private lessons teacher says that I should use my tongue to increase air speed and less of my throat but it's hard for me to do it....I need any and all help I can get, because this problem is making me want to quit playing trumpet completely. Please know that I have heard of the Circle of Breath but I haven't found any good information on it. Thank you for your time and attention.