Considering his age and what you've seen, I would suggest that you take him to see a Gastroenterologist. Does his stool have a fowl odor? Does he wake up in sweats at night? Lose of appetite? Considering his age, he could have IBD (ulcerative colitis or Crohn's Disease) if the other symptoms are also current. UC normally begins at a young age or in the elderly. I hope this isn't it. Good luck.