What Causes Blood In The Stools?

I am having regular blood in my feces, and have been having it happen for months now; at first it started as a few specks, maybe once a week, then increased. I got some anti-biotics from a doctor, but it didn t do anything to stop it. It seemed to stop on its own for some time, then happen once in a while periodically for another couple months. But, in the last couple weeks, it s come back, and it s gotten worse. There is a lot more blood than before (mostly all of it has been bright red for the entire time this has been going on), and it s at the point to where it s happening pretty much every day. I ve been having small stools or diahrrea, with very few normal, blood-free stools in between (normal stools happen about a third to a fourth of the time). I went to a doctor s office about this, and I found out I ve lost about 7 lbs since the last time I was weighed. Should I go to the emergency room about this? Thank you very much; I m really worried about this.