Ass itching and cant stop!?!?

So sometimes at night my ass itches really bad. Then once i start scratching it i cannot stop. Sometimes i get blisters from it, i use my underwear sometimes because it gives better friction and soaks up some of the juices. I also like to take my finger and rub it up my ass and get all the sweat and everything on my finger. Then i take long deep breaths smelling my finger every chance i get. Then i suck my finger to get the smell off. Is this normal?