23 yo and took plan b last week , never have had cramps on my period. now intense abdominal and back pain when on period, late onset or side effect?

May be normal: Your bleeding and abdominal pain may be normal. I would suggest taking a pregnancy test as well. If discomfort or bleeding are very significant please contact your doctor.

This can happen w : Plan b. Potential side effects w emergency contraception include: tender breasts; changes in menstrual flow (spotting, bleeding, early or late period); loose stools; dizziness; headache; nausea/ vomiting; abdominal discomfort / cramping or feeling tired. If you develop chest tightness, difficulty breathing, swelling of lips, mouth, throat – call 911. Take a pregnancy test & notify doctor if your.