monet77,
Other than pregnancy, period abnormalities can be due to many things including stress, weight gain/loss, thyroid, hormonal imbalance, infection, illness, medications, polyp, cyst, amongst other reasons. If you feel you may be pregnant your best bet is to wait at least two weeks after a missed period, and see your doctor for a blood pregnancy test as this is the most accurate way of testing. If it comes back negative, your doctor can do further testing to determine what the exact cause may be.
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