I did not have a period for 11 months. Then I had a period. Does this mean I have to wait another 12 months to be sure it is menopause?
This is an excellent question, and one that is often quite confusing to women and even many health care professionals. The North American Menopause Society (NAMS) defines menopause as the final menstrual period. Of course, you can't know if your last period really was your last until 12 consecutive months without a period (in the absence of other causes, like removal of the ovaries or chemotherapy) have passed. Since you got your period on the 12th month, you have to start counting all over again!
You don't say how old you are, but it is not unusual for women in the months or even years before menopause (called perimenopause) to have irregular periods. You may find your periods come more frequently (every 24 days, for instance), less frequently (skipping months), are heavier or lighter. They may be shorter than normal or longer than normal. In fact, it's probably safe to say that when it comes to menstruation during perimenopause, there is no "normal" anymore!
One thing to keep in mind: Since you're still menstruating, you can still become pregnant. Thus, if you're sexually active, still have your uterus and don't want to get pregnant, make sure you use some form of birth control.