My puppy is acting normal, but she had bloody diahrrea this morning!?

I have had my 9 week old beagle puppy for almost one week now and she has been great, she's the sweetest, happiest little puppy I have ever seen. Ever since I switched her food she has had some loose stools but I figured that was just a result from switching her food. Last night she had a really good firm stool and I thought she was adjusting and getting better. But, this morning she had really bad diahrrea and she had an accident in the house and we could tell that is was bloody. I am freaking out. I'm taking her to the vet as soon as they open in an hour. She is acting completely normal, no lethargy or vomitting so I really don't think it's parvo, but what else could it be???