I have an itchy bum?!

I have an itchy bum?

It only happens at night, can anybody help

This may be pinworms. As their name implies, they have sharp "points" that prick your skin and make you itch; the reason for this is they emerge from your rectum (usually at night), lay eggs, and die. They are about the size of a staple. You scratch, get eggs under your fingernails, put your fingers in your mouth, and the cycle begins again. Pinworms are easily treated with prescription medication. I know, it's gross and embarrassing. But doctors see this a lot; they're very common.