Sorry, I totally missed the comment that you're only feeding him bread. That is certainly an issue and not a balanced diet for a chicken. Also, "changing water when you can" is pretty unclear too. He should have fresh water each and every day and 24/7, along with free choice poultry feed...
Agree, coccidiosis. And if you're seeing bright red blood, the intestines are being compromised. He needs Corid, Amprol or Sulmet asap. Check out your local feed store or Tractor Supply to obtain some.