High bilirubin is caused by a multitude of liver issues.
Bilirubin is removed from the bloodstream by the liver, and then incorporated into bile and excreted out of the body via the GI system.
Gallbladder issues, including gallstones can cause it as the gallbladder collects/stores bile. As can liver failure, biliary obstructions, or as Liza pointed out meds that impact liver function (of which there are more than you can count).
Did your dr have a plan to evaluate? A ultrasound is non-invasive and would show most of the reasons I mentioned, including gallstones.....