Why is my Great Pyrenees panting, bleeding, not eating after heat?

Thanks for using Petco Pet Education Center, formerly Petcoach! Loss of appetite and lethargy can be observed with many conditions such as gastroenteritis, dietary indiscretion, kidney disease, pancreatitis, among many other possibilities. Bleeding from her vulva could be due to something else like a urinary tract infection for instance but that really depends on what it looks like so it is hard to know without an examination. I think this is less likely miscarriage or anything like that and is more likely to be unrelated to that. I recommend that you have Duchess evaluated by your veterinarian for further assessment and treatment. They would be able to check for these possibilities and others depending on the findings on exam. Treatment would be based on findings. Good luck and have a great day! Hoping for a speedy recovery!