Eradicate the cause. Stool examination and treatment would be in order.
This is probably caused by your diet. Do you eat cold cuts, hotdogs, processed foods etc? If you do stop eating them. The nitrates and preservatives will cause the itching you are describing. Lay off fried foods as well and try to exercise and drink one or two glasses of water after exercising. Take 2,000 mg of vitamin C every day for about a month and then lower the dose to normal (about 60 mg per day).