Hello,
Itchy skin that isn't accompanied by other obvious skin changes, such as a rash, is most often caused by dry skin (xerosis). Other causes include skin conditions like dermatitis, and hives, internal diseases like liver and kidney disorders, diabetes, iron deficiency anemia, irritation and allergic reactions to chemicals, wool, soaps, cosmetics and certain food. Since you are having lethargy also, so anemia and liver disease need to be investigated thoroughly.