Low vitamin D can cause weakness, muscle and leg pain, and fatigue even if calcium levels are normal, so your symptoms can be partly due to this deficiency. Your hypothyroidism and the use of Thyronorm also play a role; if thyroid levels are not well balanced, it can lead to tiredness, low blood pressure, and sometimes a faster heart rate. Excessive sweating and palpitations may also be related to weakness, stress, or fluctuations in thyroid levels. The best step is to continue vitamin D treatment as prescribed, get your thyroid levels (TSH) rechecked to ensure the dose is correct, stay well hydrated, and maintain a balanced diet with good protein intake. If symptoms like a fast heart rate or severe weakness persist, consult your doctor.