My guinea pig has been doing some squealing while peeing for a couple months now, but have not noticed any blood. Last week we were cuddling and she went pee and squealed louder than normal and there was a lot of blood in her urine. The next day I made an appointment and the vet looked at her. Did a physical exam as well as an ultrasound and X-ray and did not seem to notice anything. They concluded it could be uterine cysts or tumors. She was prescribed antibiotics and told to see how those helped. We are seeing the same vet tomorrow as her squealing has gotten louder while she pees and poops. I have noticed more of a yellowish-greenish pee. Hopefully getting her spayed will help.