Sudden onset of Rt lower abdominal pain, associated with elevated WBC count suggest a possibility of Acute appendicitis. Ultrasound may or may not be able to catch the pathology. You must get a CECT abdomen done to rule out the pathology. Acute appendicitis if left untreated may lead to perforation or may progress to appendicular mass. Acute appendicitis is a very common disease and is easily removed surgically,  but may lead to dangerous outcomes if left untreated