Hello,
This can be due to bacterial vaginosis. It is the most common cause of abnormal vaginal odor and discharge. In addition to unpleasant "fishy" vaginal odor, thin white or yellowish discharge from vagina may also be present. Diagnosis can be confirmed after pelvic examination and microscopic examination of the vaginal discharge. Treatment is by metronidazole and clindamycin. Please do not use any vaginal douches.
If you have not had your periods since such a long time, menopause also needs exploration.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.