After just one night of useing xanax, (alprazolam) antihistamines or melatonin to induce sleep, i am awake the entire night! never used to have this reaction. why?

Paradoxical reaction: You used 3 medicines at the same time to help you sleep? This makes it hard to know what's what with you. However, in some people benzodiazepines (such as xanax) are known to cause paradoxical agitation, rather than relaxation. The other question might be whether you also used caffeine or other stimulating substances earlier in the day or evening, before trying to sedate yourself.

Not the right combo: Each of these meds can help sleep or agitate. Combining them all on the first night? Melatonin is mostly benign but when used with vitamin b6 (think 5 hour energy) agitation can result. Some brands still include b6. Antihistamines are known to produce agitation in susceptible people. They learn who they are. Xanax (alprazolam) has a rapid onset but the rapid stop can agitate and cause reuse (think addiction).