How do I know when I'm entering pre-menopause ?

Watch symptoms. First off, your age may give some idea if menopause is around the corner or still years away, although this is the least reliable factor. Period irregularity, hot flashes, increased sweating, mood instability are the most frequently quoted symptoms.
Irregular menses. Pre-menopause is the time before you start to enter menopause. You may be thinking or peri-menopause, which is when you are beginning menopause. Many women's periods become irregular and may space out. Some women start with hot flashes. When your periods stop completely, that is menopause.