So what are all these green poos about?

For the past few days I have been having green poo poos! I dunno where they come from but I had my first green poo on christmas 2006 and was a little confused :s At least that time I only had one green poo, recently I have been having many. Is it symptomatic of a peptic or gastric ulcer? I haven't been feeling any nailbiting pain but I have had a general sick feeling for the past few days and have been eating a load of crap so I thought that could maybe lead to an ulcer?