ULTRASOUND can show gallstones, but it often miss them, so CT would be needed, or HIDA SCAN which shows gallbladder function.
Yellow stool can indicate lack of bile in the
stool, which is due to bile flow blockage somewhere in the biliary tree (stone, stenosis). Lack of bile in intestine causes that fats are not absorbed, and this causes diarrhea. Vomiting is often in gallblader/biliary duct disorders.
NOTE: BRAT diet is NO longer recommended in diarrhea.