Difficulty breathing through nose?

i have always been a mouth breather. i want to change to nose so i don"t have my mouth open all the time. i always seem to becongested. i talk nasally to. when i try to close my mouth and breath through my nose i feel like im choking in my throat. ive always been diagonosed with sinus infection but i dont think it is. im seeing ear nose and thoart on friday so if u think u know what this is plz help