Took plan b aug 31 & now i have lower stomach pain (like cramps) 3 days after.should i be worried or is that just a symptom? period expected sep 28

Likely a symptom: That can definitely be the hormone in Plan B having an effect on the uterine lining. Depending on where women are in their cycle when they take plan b, sometimes it can provoke a small bleed. Make sure you use protection for any other intercourse as Plan B only covers you for around 72 hours after unprotected sex. See doctor maybe for more reliable form of birth control? Good luck!