I can't stop coughing, congested and lost my voice. How do I get my voice back!?

So I was diagnosed with a lung infection about 4-5 weeks ago, I received anti-biotics and puffers because I had developed asthma. Now about 2 weeks ago, my throat started to hurt again after most of the symptoms have left, and I started to become congested, and Now for a week and a half I have been chronically coughing and I have lost my singing voice. The thing is I NEED to sing in a Christmas Eve Performance and I dont have my voice. What can I do to get it back in time!! 4 days to be exact!