thomashooten

Hi,

It is difficult to give good specific advice to your trumpet issues that you explained without seeing you in person. I would first try to find someone in your area that can give you one on one help.
Second I would concentraite on making sure that your lips vibrate easily at a soft dynamic.
When you say that playing a big mouthpiece on pic helps you play longer, that tells me that the center and efficiency of your setup is not ideal, meaning that playing on bigger equipment helps you muscle it a little longer.

Work on playing a smaller mouthpiece from time to time to help find a nice small setup with the embouchure.

Good luck,
Tom