I have found where you had posted in somebody else’s thread so have copied below:
Hello, my guinea pig started showing signs of mild indigestion on June 24, but it improved slightly after I brought her home. I was worried she might not be getting enough vitamin C, so I gave her half a piece of Aibao vitamin C grass cake and half a piece of Aibao digestive aid. Then I felt my mistake made her condition worse, so I took her back to the hospital. The X-ray showed she had severe bloating and food buildup. We started using simethicone, probiotics, cisapride, and added 1 milliliter of sesame oil, which improved her condition. She passed a lot of stool, some very small, some extremely dry, and some with sharp edges, but she passed a lot of stool. Since my mother didn't understand, she picked up the feces each time, preventing her from eating her own blind intestine feces. Around June 28, I noticed bloodstains on her pad and examined her feces closely. Among them, there were three with very deep red stains, but they were hard to notice because her feces were well-formed. Since I saw the bloodstains, before going to the hospital, I switched to a different brand of probiotics and gave her half a dose. About an hour later, she defecated again, but the stool looked very healthy and showed no signs of blood. Nevertheless, I took her to the hospital for a check-up. The X-ray results were normal, and the doctor noted that my pig was defecating normally at the hospital, so he did not perform any stool tests and advised us to observe at home. If there was further bleeding, we should undergo an abdominal B-scan. However, the next morning, I noticed a small amount of blood again, though only a trace. So I took her back to the hospital for another abdominal ultrasound, which showed she was very healthy, and they sent us home again. But I didn’t want to put her through any more tests, So after she defecated, I took the stool samples to two hospitals for testing. Both said there were no issues. I showed them the ultrasound images, and both hospitals also said there were no abnormalities. One mentioned there was a small amount of gas in the stomach, possibly due to stress and fear, while the other noted a small amount of fluid in the stomach, but neither was a cause for concern. Both advised me to go home and give her probiotics and feed her normally. However, I was very worried about my little one because no abnormalities were detected, but I had read online that guinea pigs can have internal bleeding. Internal bleeding is highly unusual. What should I do? Chinese veterinary medicine for guinea pigs is truly inadequate. I informed the doctor about the blood in the stool and provided previous photos, clearly explaining the situation. However, the doctor did not perform a stool test or B-scan during my first visit and subjected my baby to multiple procedures. I am heartbroken. I hope you can help me. Please, I beg you. I have no choice but to reach out to you. I don't speak English, so if possible, could you please contact me in Chinese? If Chinese isn't available, my partner can speak English, so either language is fine, but preferably Chinese! Thank you so much. Please help me!
Guinea pig health is a steep learning curve. Does your piggy have dry skin on her nipples? That can be a sign of hormone problems. How old is she? If you can take a fresh urine sample to the vet, that could be a useful diagnostic test. If you put her in a plastic base carrier, after a few minutes she should pass urine. If you can extract it quickly to avoid contamination that is best. Does she have any large lumps in her abdomen? Is she vocalising pain or hunching over when urinating? I hope the problem can be solved 
Keep going back to your vet if she is still passing blood.
