My dog used to experience similar problem (not as frequent though), the vet suggested mixing about a tablespoon of metamucil in her food and using anti-itch cream. The vet said to get anti-itch cream for baby diaper rash (I use regular vaseline and it works), put some cream on your fingers and apply on dog's anus (one quick sweep when she is standing). Do this before walks or else the dog will lick it off. I do both for a couple days when I see my dog scooting on floor/licking her butt and her symptoms go away. Hope this helps.
Jenn
Jenn