My 6-month-old dog is weak, not eating, losing weight, bloody stool.

Poor Luna! She could have an infection (parvo, etc) or a parasite. Since she has bloody stool and is lethargic, she should be examined by a vet to determine the cause and treat. Your vet can test a stool sample to help diagnose and then prescribe medications to treat the problem. She might also need some fluids to prevent dehydration. Hope she gets better soon!

This sounds more like your dog has a chronic gastro-intestinal problem such as food intolerance, gastritis, chronic or acute pancreatitis, food indiscretion, or even a tumor, liver disease. He also may have a chrionic infection somewhere, e.g. in his prostate, which could be the cause of the blood in his urine, or kidney disease. The signs are too unspecific to pinpoint a cause, so you need to take Potato to your vet for an exam and blood work, and possibly xrays. Please make an appointment right away.

This is an absolute emergency and requires urgent veterinary care. GE may have an intestinal obstruction or severe gastroenteritis and will require urgent treatment to investigate the cause and stop the vomiting as well as replacing the lost fluids

All of those combined sound like a very serious issue that should be seen by a veterinarian in person immediately. Toxicity, neurologic issues, illness, vestibular issues, muscular problems, etc can all be potential causes, so it is best to seek help from a veterinarian in person or a local ER clinic ASAP.

Poor Lightening. He could have parvo, hemorrhagic gastroenteritis, may have eaten something rotten or toxic, or could have a foreign body. His symptoms are a medical emergency, and cannot be treated at home. Please take him into a vet immediately.

Cookie is experiencing very general symptoms of disease, these symptoms could fit almost any internal condition, it could be due to a serious condition such as cancer but it could also be due to a foreign body in the stomach for example, from the symptoms described it's very hard to know. i would recommend taking him to the vet as soon as possible in order to get him checked, if he doesn't show any other obvious symptoms during the examination, a blood test and possibly an ultrasound will be needed in order to try and find out what is wrong with Cookie .

If Dots is vomiting, losing weight and not eating, he needs to be evaluated by a veterinarian as soon as possible. The veterinarian will likely recommend bloodwork and x-rays to start. Possible causes for his symptoms include an intestinal obstruction, inflammatory bowel disease, infection, liver disease or even cancer.