My dog is itching right above the tail what is the problem

Have you checked for fleas? Fleas like to hang out on the rump of a dog.
Run your thumbs up the back against the coat and check for live fleas or what is called flea dirt.
Flea dirt looks like tiny black specs on the skin and fur.
You cannot check for worms yourself, but you can take a stool sample in to your vet and have them check.
Another option could be the anal glands, but you'll need to get the vet to check those too.