acute rectal bleed and left lower back and abdominal pain

Got severe abdominal cramps, diaherrea. I thought I just had flu or food poison. Diaherrea quit, next morning just blood came out in toilet. Went to emergency. Blood test all came back pretty normal, went to restroom there and was just geled blood. They took sample, tested was negative for e coli, etc. Much discomfort in left lower back and abdomen. 2 days after leaving hospital still a lot of blood in stools and pain. Had a colonoscopy 7 months ago. 1 pre cancer polyp removed but everything else was good. What is wrong with me. The Doctor at the emergency room took no test, just said it is probably a bleed from a major artery or vein from a diverticulae and put me on 3 days of antibiotics. How does he know without any test?  I'm really scared. I'm 55 years old. I am going to try to get into my GI doctor, but it's so hard to get in fast. All this pain and blood is scaring me big time.

[CrisC]

There are a few tests that I'm wondering if they ran. First off, I'd assume they checked your hematocrit and red blood counts and found them to be within normal limits. I'd verify that if I were you for a sense of self assurance. If the bleeding persists or increases you should have some diagnostic tests done such as a nuclear medicine scan. A NM scan will show if there is active bleeding. If there is, the bleeding vessel can be embolized in the angiography(interventional radiology) dept.
Did they do a CT scan while you were there?

[cony]

Thanks for the response. Yeah, they ran blood test and I was within normal red count. No other test were done. I was kind of surprised they didn't give me more test. I'm hurting and I don't know what to do.