It could be delusion of parasitosis or generatised pruritus secondary to any underlying disease. First get all routine blood tests done(CBC with peripheral smear,
LFT RFT serum
lipid profile,
thyroid profile, urine routine, chest x ray pa view, USG abdomen and pelvis). And also consult psychiatrist to rule out delusion of parasitosis. Use calosoft plus lotion temporarily and tab Dazit M whenever you have itching.