Menopause is a time that presents with many challenges, one of the most common of which are the hot flashes and night sweats that are present in the vast majority of peri-menopausal and post-menopausal women. Most people will report that they decrease gradually over time (although they almost always last at least one year), and many will have a complete resolution by 5 years time.
That being said, almost 10% of women will still complain of intermittent hot flashes in their 70s, which would be (usually) at least 10 years after their last menstrual cycle. Some anti-depressant medications are used to help with some of the symptoms, although they are less effective than the first line treatment of hormonal medication, of which there are many options. Most people will have resolution of their symptoms when they begin hormonal therapy, and many will not have hot flashes that return after slowly tapering off of the hormones later.
We are unfortunately not sure what causes hot flashes, but it appears to relate to how the body adjusts it's internal temperature. If you are having symptoms this long after your last period, however, you should discuss them with your OB/GYN or primary care doctor