My dog has been throwing up yesterday all day long. I took him to the vet, they took x-rays nothing was seen. After 4 or 5 hours he starting peeing blood. I rushed him to the vet but they still have no answers for me. Any ideas on what it can be?

Unfortunately it could be a lot of things, from a kidney infection to trauma to, yes, parvo. Hopefully you left him at the clinic so they could keep him hydrated while the diagnosis is processed.

It could be. There is a test they should be running if they suspect it.