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.
Oral antihistamine, such as Benadryl can be used for itching. You should take a comfortably cool bath and wear smooth-textured cotton clothing. You should choose mild soaps without dyes or perfumes and use a mild, unscented laundry detergent when washing clothes, towels and bedding.
Please take a second opinion from a dermatologist if the symptoms persist. He/She will start with the specific medications. If an internal disease is found, whether it's kidney disease, iron deficiency or a thyroid problem, treating that disease often relieves the itch.
I sincerely hope it helps. Take care and please do keep us posted in case you have any additional doubts. Kind regards.
Allergy to polyester does
Maybe more. But that is all I know of. Then again, my specialty is allergies to synthetics. And I say polyester is the one for you may have gotton some new panties with it, or polyester pants?