my throat burns after i play the tuba for too long???

ive been playing tuba for about 6 years and ive always noticed that when i play for like 3 or more minutes straight (no long measure breaks) my throat starts hurting really bad?? and like gross saliva builds up in my throat idk if thats tmi but. i think its because i cant swallow??? im not sure i had cleft palate surgery when i was a baby if that matters??? does anyone else have this problem ive asked my band director and he said hes never heard of it