The squealing while peeing is almost always a stone. I am surprised the vet did not find one on the xray.
I am so sorry your guinea pig is sick and in pain.
- And got the T-shirt
A bad infection in the GI tract could cause bleeding, as could an abnormal growth. But in most cases, the kind of bleeding you're describing is from the reproductive tract.
There is a definite area of roundness in the abdomen in the top two pictures. I don't think this is bloat (would be more abdominal IMO). It seems awfully large for ovaries. What does the vet think?