It happens to many people . . . but I don't know whether that makes it normal.
John Lee (What Your Doctor May Not Tell You about Menopause and What Your Doctor . . . Perimenopause) and Christiane Northrup (Women's Bodies, Women's Wisdom and a book specifically about menopause that I have not read yet) both have good books out about menopause. They talk about the various hormonal changes and natural ways to compensate for them. Doctor Lee's book on perimenopause was brief and very concise, so one of his books might be a good place to start.