Avoid carbs and eat more veggies. Also go to the bathroom more often. If you hold your turds they become hard and hurt your asshole.
Also, don't spend more than 3 minutes on toilet, sitting on it for too long destroys your asshole.
Next time you're in the shower check your butthole. External hemorrhoids can be felt.
Edit: don't wear jeans or boxers that squeeze your butt cheeks together.