I had intercourse and took plan B 24 hours later. I had intercourse again the following day & as a precaution I took plan B again. Within the 24 hour window. I had gotten my period a week later (which was earlier than my expected time). However, the period lasted 3/4 days rather than the usual 6/7. I am now experiencing lower abdominal cramps and slight naseau. Should I be concerned?