Concerns for Blood in stool

I am a 33 year old man, who has had a clean bill of health.  However, I started noticing blood in my stool since summer of 2008.  When I would stool and wipe I would notice blood on the tissue and in my stool.  This happened for about one month.  I seek medical attention, and as a result, there was some test done on my feces, which came back negative to colon cancer. I was given some medication and the blood in my stool went away. However, I am presently bleeding again when I stool.  This has been going on for the past week.  I am not sure what is going on with my body and am writing for advice to my dilemma.  

Thanks alot for your prompt response to this matter.

Eli
January 19th 2009