My Dog Has Chewed His Hind End To Raw Skin And Bleeding. Im Giving Him Benadryl But He Wont Stop. Now He Is Acting So Strange And All He Wants To Do Is Lay Outside?

I had a puppy once that did this, he had parvo... The nerve endings in his tail went dead for some reason when he got parvo, he eventually gnawed his tail so much the vet had to amputate it... The vet is expensive I know but he will keep chewing and gnawing until you stop him!

We are having the same problem with our Australian Cattle Dog. I just got back from the vet with him and he has an allergy to a type of grass. He sits up all the time so his bottom and tail is more exposed to the grass tips which causes him to itch and break out.
Maybe that's the case with your animal.