Black stool indicates bleeding from the upper part of the gastrointestinal tract, due to bleeding ulcer, gastritis, or esophageal tears resulting from the violent vomiting.
Thin stool usually means presence of intestinal blockage like colon polyp or colon cancer.
Bright red bleeding in toilet and over the stool may result from internal hemorrhoids, polyps, cancer and diverticulum.

The constellation of your symptoms is very suggestive for more serious gut condition, so, it will be a good idea to see your physician as soon as possible.

Best wishes!
Marija