My 3 Month Old Daughter Has Bloody Bowl Movements For The Last 8 Weeks. What Could Be Causing This?

my 3 month old daughter has bloody bowl movements. shes had them for the last 8weeks. Ive taken her to the hospital twice and dr offices almost every week since this began. at first they thought it was a milk based formula allergy but shes been off of that since this started she is now on nutramigen. she has no other symptoms of anything but blood. the blood is no longer just strictly located to the stool but is being absorbed strait into the diaper and on her legs. the bloods color switches from bright red to dark. shes had x-rays done that haven't shown anything that could be causing this.