Hi! history of diabetes with obesity and complaining of headache, vomiting and giddiness points toward hypertension, so first of all check the blood pressure and If BP comes high then first try to control it by altering lifestyle, diet control, decreased salt intake, start exercise and start drug with diuretics and other anti hypertensive if required. These symptoms might be due to peptic ulcer disease or gall bladder stone, to rule out these pathology, endoscopy, ultrasonography and x ray can be done. As you give history of diabetes , so keep on checking blood sugar level at regular interval and maintain it within normal range by proper preventive measure or antihyperglycemic drugs if required. As for your information I want to tell you some side effect of ranitidine as.headache , dizziness, hypersensitivity, impotence, vertigo, halucination, somnolence, gynecomastia etc.