I have a national concert (a series of shows) in less than a weeks time. I have been practising hard for the same suddenly as the day is approaching my voice is sounding more and more strained and even flat at times. I cannot sing in the scale I started with and with even an hour of singing my voice starts to feel sore and tends to break. There is no vibrato at all. I have tried gurgling with salt water and also tried taking steam. What can I do to keep my voice in place for the show next week?