Why is my bum hole so often itchy?

It started around three years ago and gradually got worse and more frequent. I tried using creams for piles but they didn’t seem to work. Eventually it eased off but in the last year ago has started again. It can happen at any time of day or night. I go to the loo once or twice each day, usually without any difficulty. I sometimes suffer from wind. Occasionally I draw blood when I wipe my bum but not often.