Hi. Thanks for your query. Noted the history, albeit short and specific. You have recently changed your diet and have burning sensation at the top of stomach and bottom of breast bone, mainly prominent between the meals, you have cut out a lot of sugar and fat; wants to know whether this is due to an ulcer. Your history is surely suggestive of gastritis and associated things. There can be an ulcer too. But this can be diagnosed only by an upper GI Endoscopy. Hence I would advise you to consult a Gastroenterologist for consultation, investigations and proper treatment. If it is taking a long time for an appointment with a Gastroenterologist, consult with your regular Doctor for clinical evaluation and get a prescription of a PPI like Omeprazole, an antacid, Domperidone, Symptomatic and supportive treatment. Also get the blood, urine and stool test, particularly for occult blood.