Many things can cause this: * Believing your pregnant can somehow result in a woman feels physical symptoms or believing she is having symptoms of pregnancy. * Hormone imbalance. * Birth control. * Worrying excessively about being or falling pregnant can also cause physical symptoms to appear. So basically apart from the hormone imbalance and birth control, its all in the power of the mind. Psychologically believing something very strongly or worrying about it constantly can cause physical symptoms to appear but these symptoms will only be noticeable to the woman.