PLEASE HELP, What can I eat/drink to get rid of this phlegm in my throat?

[THE *only* lePineyapple]

So I have a musical showcase to do in two weeks, but I always have this phlegm in my throat (I also have a nasal accent sometimes and can never fully breath clearly). For this reason I have voluntarily been an alto throughout rehearsals, but now I have to sing "Notice Me, Horton" and I can't hit high notes because every time I try to switch from chest to head voice, the phlegm gets all in the way and I sound like a dying cat. Same goes for when I try to use falsetto. Are there any foods or drinks I can have on hand to get rid of this mucus both for practice and on the "big day"? I'm not really into taking over the counter drugs because I'm already on six different medications for a health condition I've got, so natural stuff would be best.

And I know dairy causes mucus, but I can't stop eating dairy because I need a high calcium diet for one of the meds I'm taking which causes bone deterioration.

Thanks.