I lost my voice, what should I do to get it back and what should I avoid doing? I heard wispering is bad and makes it worse, is that true?

Laryngitis. If you have lost your voice, the best treatment is voice rest -- avoid talking and whispering as best you can -- you can try tea with honey and otc Guaifenesin as well, but symptoms may last 3-5 days.
Voice loss. Your voice loss may be due to a problem with the vocal cords or inflammation in the larynx, possibly due acid reflux, upper respiratory infections, allergies, smoking, inhalation of irritants, or overuse of your voice. Try not to talk too much unless you really need to and avoid whispering. Whispering can strain the vocal cords more than speaking does.
Rest is best. Voice problems are comon and very important. Most of us can't work or play withuo ta good voice. Whispering puts even more stress on your voice so it's a 'no-no'. Most injureies come from overuse so rest your voice if you are able. Consider seeing a voice specialist (laryngologist) at an ENT office if rest doesn't make it completely better or the problem lasts more than 2 weeks. Get well.