Benedryl will help with the itching and will help soothe if it's allergy related but it won't cure it if it's a fungus or bacteria or mite infestation.
I'd try some bag balm on it. (tail area, I'm sure the lip is just raw from digging at the tail...that should heal on it's own)
PM me in a week or so if it's not any better and I'll e-mail the pics to my sister...She's a great dane guru and is my first call before the vet. She knows more dog stuff than most "normal" people should. (BTW...She's got 7 Danes..IN her house.