This is what happens to my dog Grace when she breaks out into hives. They are usually VERY itchy, you can tell if you go to itch them for her, she is just so grateful. When we go into the vet (when they are BAD) she gets a steroid shot (I limit those), some hydroxyzine and we also use a topical ointment as well. The OTC benadryl spray seems to be the least messy and most effective for her. You can use benadryl as well but when they get bad I find they get under control much quicker with a vet trip. It could have been the soap she was groomed with, the shots, anything really.