Hi Noelia,
I was a vocal major in college and my professional voice teacher once told me about this, which I tried and it worked. It does not taste good but it works. Mix 2 TBS of cidar vinegar and 2 TBS of lemon juice with 8 oz of almost boiling water (very hot but cool enough to drink - like hot coffee). Drink as quickly as possible. You can add more lemon juice to help cut the taste of the vinegar but NOT more vinegar. The combination of lemon juice and vinegar work together to strip the vocal chords of crud, which takes the stain off the vocal chords. I drank it before my sophmore recital when I had an upper respiratory infection and was able to sing through my recital with no problems.
Another very helpful treatment I use now is cough drops with tea tree oil. I purchase them from a wellness company call Melaleuca. You can only get them there. If you're interested in that let me know and I'll tell you how you can purchase whole sale.
Good luck!!
K. Woodlief
www.LiveTotalWellnessToday.com