Past three days been extremely itchy all over body, primarily arms and legs. No rashes, etc. No new changes at all. No allergies. What can be cause?

May be hard to find. About 50 % of cases of itching without rash, one is not able to figure out the cause. Of course, the common allergens are something inhaled that the histamines in the body react to; or some new perfume or scented lotion, deodorant or something else new used on skin. Suggest taking an otc antihistamine daily, take only lukewarm showers. Will likely go away in 2-3 weeks. If not, the usual: c the doc.
Lots of things. Many potential causes, and i'm sure i'll overlook some. Could be a very early infestation with scabies, exposure to some irritant, seasonal allergies, dry skin, or pregnancy. It could be something more serious like liver dysfunction. I'd see my gp for an exam.