Conditions Possible UTI or Behavioral Issue?

Urinary tract stones. I'd bet the farm on that, or a UTI. And it needs a quick vet visit. Some stones can fall down into the urethra and block it, creating a real medical emergency. If you're lucky, and if you've got a good vet, they may be able to manipulate the stone out.

Nothing that looks like pain in a guinea pig is behavioral. Sounds like pain, maybe, if they're being annoyed, but whimpering and straining are medical issues, not behavioral.

Her pee is normal in color and no odd texture. If I'm holding her or if she has been in a comfortable position and she pees, she doesn't cry or strain. Only after she has been pushed around by her sister. That was why I was questioning the behavior.

Went to the vet last night. Spent 2.5 hours there, had an x-ray and urine sample analyzed. They wanted to do blood work on her, but couldn't get enough blood to run the test. She did not have any stones, but there was "sludge" in her bladder. Sludge is a concentration of calcium that sits in the bladder and is uncomfortable to pee out. Its not a stone, but if left untreated it could block her urinary tract. They were also concerned about the color of her urine. It was super clear which the vet said, might indicate kidney or liver disease (or could be part of the sludge issue - hard to tell without a full panel of blood work). There was also a high red blood cell count in her pee, which is essentially blood in the urine, but its not showing up as a red color. So they want us to come back and have blood work done, especially if she does not improve on the antibiotics.

In the meantime, Ginny can not eat anything with high values of calcium like kale (which she will be very sad about). She was given fluids at the vet and was sent home with Bactryl. We are to give her barley water and keep her super hydrated to help her pass the sludge.

If the Bactryl does not help her in 10 days, the next step is to look at her kidneys and liver.

In regards to my original question about Ginny's behavior (crying when she peed only after her sister pushed her around - not when she was in a comfortable situation): the vet said her sister aggravating her probably brought down her defense wall a bit. Therefor, the irritation when Ginny peed was magnified. So we were lucky and got an even earlier warning sign that something was up. If Ginny was not upset by her sister, she would have masked her discomfort longer, and we would have been in a much more dire situation.

Ginny was a champ at the vet! I was so proud of her When we got home, all three of us were exhausted! Ginny's sister, Cheri, was very happy to have her home, and kept trying to groom Ginny. Poor Ginny, just wanted to sleep, and did not want to be touched. It was very upsetting for Cheri that Ginny did not want her attention - ah the drama of piggy life.

This morning Ginny is pretty much back to her usual self. I am keeping a close eye on her, and will be seeing how she takes to the barley water later today.

Bactryl? Do you mean Bactrim, or Baytril?

Barley water? I've never heard of it? I hope Ginny feels better and her sludge goes away!