Unfortunately, it is very difficult to tell how long symptoms will last as the menopause is different for each woman.
Some women may have very few symptoms for a short period of time whereas others may have lots of symptoms over a number of years. However, symptoms can also be linked to your general health, diet and stress levels so looking after yourself well at this time is really important.
Caffeine can trigger hot flushes and night sweats, so keep caffeine intake (coffee, tea, fizzy drinks) to a minimum, especially in the evening and ensure that you are drinking plenty of water to rehydrate yourself. Dehydration can cause feelings of anxiety, which then makes flushes and sweats worse.
Fluctuating hormones can cause night sweats but stress can be a big issue as well so you may find taking a magnesium supplement helpful.
Make sure, too, that you are having a snack before bed. Low blood sugars can often be a contributory factor, just make sure it is not a sugary one but more protein/carbohydrate based such as nuts and seeds, a plain yogurt, or an oatcake and cheese.
Also, it is important to check with your doctor as they can be caused by other factors such as low iron, low thyroid or low vitamin D and your doctor can test for these.
In the meantime you may find sage helpful, this has been traditionally used to help with flushes and sweats. To help night sweats, I recommend you take this one-a-day tablet with your evening meal.