Help with trumpet skills?

OK, so I've been playing trumpet for about a year and a half. I'm first chair, so I've been getting all the high notes and every time I practice, during some part of the song, my lips will hurt and I start to die out, or go from buzzing to blowing or go from right note to messing up, how can I keep up, better yet, what should I practice to improve? Were playing songs like Semper Fidelis. So what do you think?

Help with trumpet skills?
I play trombone and I was first chair, when we did chairs, but I still play 1st part. I had that problem in 7th grade....right after beginning band. I could hit the high notes, but afterwhile, my lips would hurt and I would die out. All I can say is I kept practicing and playing with my band, and it is all better now. I'm an 8th grader. Just keep practicing what you always do, but do long...steady tones on high notes when you practice...don't forget the belly breath!
Reply:sounds like your lips are getting tired. what would help you build some endurance is long tones. practice long tones on a scale to help build endurance. pick a scale which you find reasonably challenging and practice going up and down the scale. if you start to get too tired playing the scale, then switch to a lower scale to practice, or take a break for a few minutes and come back to practicing after a short break.