It could be possible that a gallbladder still show up normal in an ultrasound when symptoms are present?

Yes, under two: Conditions: acalculous cholecystitis and biliary dyskinesia. And although ultrasound is a very accurate test for stones, it is close but not 100%. In a very small percentage of patients, gallstones are present on surgically removed gallbladders even when the ultrasound was negative. Biliary dyskinesia is a condition where gb does not empty properly and causes pain. Ask your GI specialist.