There can be a lot of reasons, other than pregnancy
for your periods to cease. Have you recently started or stopped birth control pills? Have you become more physically active, and lost weight?
Many times your body will go through hormonal
changes, and it may take some time for your body to adjust to its new "normal". Or if you become too thin, your body doesn't have the reserves to produce a normal period.
My periods were never "normal". I've always been thin and sometimes would go months with out a period. It does make you very nervous, but not everyone has periods every month. And, we still survive.
Just to ease your mind, make an appointment and see your doctor. They are the only one that can determine if there is anything wrong.