Hello,
Often green stool is related to foods you have eaten, such as dark green leafy veggies. It can also be caused by rapid transit time of food through the colon.
You may have gastritis or gastroenteritis. In either case, all rectal bleeding needs to be evaluated by a physician. Click on the link:
http://www.mayoclinic.com/health/rectal-bleeding/DG00015
The signs and symptoms of gastritis, which are often relatively mild and short-lived, include:
A gnawing or burning ache or pain, similar to indigestion in your upper abdomen that may become either worse or better when you eat
* Nausea
* Vomiting
* Loss of appetite
* Belching, bloating & gas
Gastroenteritis, which is also called stomach flu, usually results from a viral infection of your intestines. Signs and symptoms include diarrhea, abdominal cramps, and nausea or vomiting, as well as indigestion. Symptoms of gastroenteritis often resolve within a day or two, whereas the discomfort of gastritis may be ongoing.
Here is some info, let me know what questions you may have:
http://www.mayoclinic.com/health/first-aid-gastroenteritis/FA00030
http://www.mayoclinic.com/health/viral-gastroenteritis/DS00085
http://www.mayoclinic.com/health/gastritis/DS00488