Sinus Medication Solution

i’ve had a sinus infection for the past few days. i’m feeling better now, but breathing through my mouth all day has taken it’s toll on my singing voice and throat. my throat feels raw, and i’ve also been coughing. i have a very important audition on wednesday, and i really need it to be in perfect shape. is there any kind of quick-fix or something that could help? i appreciate any help!