How to tell if it's a sign of pregnancy or symptom of taking morning after pill?

Yes: There can be side effects when one uses emergency contraception. Emergency contraception symptoms can include spotting or bleeding, changes in menstrual flow or your period may be late or early. It can also lead to nausea, abdominal pain, breast tenderness, dizziness. If your period is more than a week late take a home pregnancy test and follow up with your medical provider / gynecologist.