Sounds like an allergic reaction to something. That happened to my boxer before. I gave her a new food and she got bumps all over. I took her to the vet and the doctor said she either had an allergic reaction to something or she possibly got bit by something. They 'ran some tests' and found nothing. I got a nice sized bill for them telling me that can't find anything. I suggest waiting a full 24-48 hours and if the bumps are still there then take her to the vet.