Hello, I have gone through your query and understand your concern. There are plenty of causes for recurring chills without fever. As you had the similar attack last month, I suspect some possible causes and it need further workout. 1. Hormonal changes or Hypo or Hyper thyroidism As one reaches the perimenopausal or menopausal age, there are changes in the hormonal levels. No you are also taking the Progesterone and estrogen as well. These can be ruled out by checking these hormone levels including thyroid profile in blood. Whether the hormone you are taking are sufficient or you have to reduce the dose, can be decided by checking these hormonal levels. 2. Side effects of the drugs As you are taking Synthroid, Progesterone, Estradiol, Lisinopril, the side effect any of the drug may cause these sudden chills. As i already said, Please check hormonal levels. 3. Hypoglycemia. You may have diabetes and at times your blood sugar may drop. These may reflect as chills without fever and then eventually your body may adjust to the low sugar levels. Other possible causes are Anemia and Malnutrition. As one ages, Anemia and Malnutrition are common problems due to poor non healthy diet, stress etc. Your Hemoglobin levels may be low. As you are taking multivitamins, you need to take Iron tablets in addition. Eat Healthy diet. Drink plenty of water. Investigate for the above said causes. In addition have regular annual health check up plus do pap smear and check for any breast lump to rule out any cancer regularly. Hope this helps. Please write back for further queries. Wishing you good health.