ITCHING ALL OVER THE BODY

A 23 year old male came with complaints of generalised itching all over the body. His itching occurred intermittently during the day and he became more aware of the itching during the night. He has no interdigital lesions. He has taken full course of ivermectin and applied permethrin lotion for scabies previously advised by his dermatologist but the symptoms do not seem to resolve. What could be the possible etiology? Kindly suggest further management.