Insulin is usually started when the blood sugars are uncontrolled on optimal oral diabetic medication in diabetic patients. There is no reference range at which the insulin should be begun because diabetes is an individualized treatment, so it depends on the patient clinical profile and is blood sugar levels. Your frequent urination could be because of uncontrolled diabetes or associated UTI. Please check your blood sugars and urine routine and consult an endocrinologist for further management. Thank you!