My 3 year old has had yellow diarrhea for 8 days along with a a lot of runny blood and stomach pain. tests came out clean, no doctor can diagnose her.

Testing/fluids: I would suggest that keeping him well hydrated, avoid dairy products with the exception of yogurt containing live cultures, until the diarrhea resolves. Your doctor may have already sent bacterial cultures, a screening for parasites, and c. Difficile and e coli toxin screening, however you can check with the pediatrician's office regarding these tests. I hope that this helps.