How long after taking EC should "symptoms" including mild cramping and "butterflies" in lower abdomen stop?

You may be pregnant. Butterflies in your stomach sound like you may be pregnant. If you haven't checked yet a urine pregnancy test or go to see a doctor immediately. Emergency contraception only works about 70% of the time since it only works if you take it in your cycle before you've ovulated. It also doesn't work well for a woman with a BMI greater than 25.