Managing diabetes mellitus along with vitamin D and iron deficiency requires a balanced and consistent approach: continue your insulin exactly as prescribed and monitor your blood sugar regularly, as good glucose control helps your body use nutrients better. For deficiencies, take vitamin D and iron supplements only as advised by your doctor (iron is best absorbed on an empty stomach or with vitamin C, while vitamin D is better taken with food), and include foods like green leafy vegetables, legumes, nuts, eggs, and fortified dairy in your diet. Also, get safe sunlight exposure for vitamin D and avoid taking iron and calcium together as they can interfere with each other's absorption. Regular follow-up tests are important to track your sugar levels and correct deficiencies. Inform your doctor if you feel fatigue, weakness, or dizziness. With proper medication, diet, and monitoring, all three conditions can be effectively managed together.