A 12-year-old girl complains of general weakness, rapid fatigability, and intense periodical pain in her upper abdomen. The pain occurs immediately after eating or 15-20 minutes later. Periodically, she develops pain at night, sour eructation, and vomiting with just eaten food. According to the patient's medical history, she has been suffering from chronic gastritis for the past 3 years. The patient's father has a long history of peptic ulcer disease of the duodenum. Objectively, the patient's skin is pale, the tongue has a white coating, the abdomen is soft and painful in the epigastrium during palpation. Mendel's sign is positive. What is the most likely diagnosis in this case?