And what is the difference between xanax and clonazepam?
Hydroxyzine is an antihistamine with anti anxiety properties. It is not as powerful as the benzodiazepines (BZDs) Xanax (alprozalam) and clonazepam (Klonopin), but might be strong enough so is worth trying first. It will take 1-2 hours to reach maximum effectiveness, as will the BZDs. It's half-life is about 24 hours.
Xanax is a short acting BZD with a half-life of about 11 hours. Clonazepam is a long acting BZD with a half-life of up to 50 hours. If you only need a BZD occasionally, say 1-3 times a week then Xanax would be the better option, but if you need to take one every day then use the clonazepam.
Have these meds been prescribed to you? If so, what instructions were you given?