How do I make my soprano voice come back?

I was sick two weeks ago, and now I have just a bunch of mucus. I lost my talking voice and got it back last week along with my singing voice. But only my low and middle voice. I have to sing soprano for Sweeney Todd, and I can't now because it's gone. Every time I try to get into my high voice, it sounds like a whisper that isn't even music. How do I fix this in the next few days?