My puppy has bloody diarrhea??!!?

Yesterday I took my 2 month old puppy outside to use the bathroom. As always I watch her go..I thought she was peeing. But the pee looked weird and I saw some blood. I looked around to her backside and saw that she was pooping!! It seemed she had diarrhea but it was transparent and gooey looking and I saw some drops of blood come out. I called my vet and braught her in. But they couldnt kind anything wrong with her. I've changed her puppy food, but now she wont eat much and she's still bleeding. What else could be the problem?? We're taking her to another vet tomorrow to see if they could find out whats wrong.