Anal glands or allergy were the first things that sprang to mind.

Flea treatment and worming never hurt for ruling out. You've said you're going to the vets anyway so you can have the glands emptied. If that doesn't work, look to food. An elimination diet is the cheapest way to go with working out what causes reactions in respect of food

I'm not thinking food allergies because I'd think the dog would be scratching all over, not just the tail end. My boy has several allergies, and along with the pitiful hair loss, goes relentless scratching all over the place.

Hi shay.
Did worming help lyric? I too have a jrt cross who done this, took him to vets a few times as he had bad lesions on his back, we worked out he's allergic to commercial foods.