What Causes Entire Body Itching?

I facing a whole body itching all the time its like stabbing with the needles, a bugs scrawling on the body.some time if we press the body parts very hardly the sevearity is more.if we dont its less,its occuring all the time.its commenly more on the sexual parts.I could not sleep well at the night times.I am the regularly using the tab. cetiricine for temporary control.what is the reason behind that pls give me a solution.