What causes abdominal bleeding/bloody stools?

Apparently my dad has been having abdominal/rectal bleeding and bloody stools for weeks paired with severe pain in his kidney area, and hadn't so much as called his doctor. Yesterday, he woke up at 3am in severe pain, went to the bathroom and was just gushing blood. He went to the hospital, but the doctors still have no idea what's wrong, even though they have run some tests. He has multiple sclerosis, and has for years, but somehow I doubt this is related. He only takes one prescription, a medication to treat the MS called copaxone, but no other prescription, otc or homeopathic medications. I looked up copaxone yesterday, and his abdominal problems are no where in known side effects (and I read pages and pages of information on this drug). Since his doctors don't seem to know anything, does anyone else know of possible conditions that might cause that? It really worries me that he's having problems in his GI tract. I have Crohns disease, and I know what it's like to have extrme pain in there (horrifying) and blood coming out both ends. I wouldn't imagine he has Crohns, but him having the same kind of pain and bleeding paired with the pain from his MS, that's gotta be horrible. Any ideas? More to ease my mind than try and play doctor to diagnose him.