My dog keeps bleeding from her mouth and gagging. What should I do?

If Lucy is continually bleeding from the mouth, I have to disagree with your vet's assessment that everything is fine. There has to be some cause for the bleeding. Common causes of bleeding from the mouth would include some sort of trauma, dental issues, primary bleeding disorders (usually causing bleeding from the gumlines and inner lips), or some sort of bleeding mass inside the mouth that has ulcerated. I would be curious to know what kind of blood test was run. Was it a test to look at organ function, or was it a test to actually look at the blood's ability to clot appropriately? If your veterinarian did not perform an extremely thorough dental exam and oral exam, I would return and insist on it. You could also visit your local emergency clinic or another veterinarian to get a second opinion. Depending on the level of bleeding currently, you may want to go to the vet now rather than waiting. Since I can not physically see your dog, I always have to recommend going to the vet now in cases of active bleeding. Hope this helps.