Hot Flashes Not Menopause

I had my ovaries removed in June, and nearly two months later I started having hot flashes, and I wake up at night sweating. I thought the hot flashes will not occur during menopause, and not after.
And if this is the reason, how long it normally last?

Symptoms of menopause can be reduced after going through it, but that does not mean they will definitely be gone. In fact, you are always at risk with symptoms associated with menopause, but lifestyle and dietary changes should help you feel less of these symptoms. You should see your doctor and tell him about what you feel.

I totally do not know how long

Yes quite reasonable. go to your OBGYN and get some drugs, it will help

Menopause symptoms rarely disappear. Frequently, they persist in old age. I suggest you investigate the bio-identical hormone personally tailored to your individual requiremnents. Believe me, it can do wonders.