I had unprotected sex a week ago the day before my ovulation day and 11 hours later i took a plan b early in the morning on ovulation day. yesterday i started having the urge to pee even after going. can it be a side effect from plan b?

I would suspect you have acquired a UTI after the sexual encounter rather than blame it on the plan B. If the symptoms continue have it checked.

Agree with Dr. Ferguson. You should see your doctor for a urine test and/or culture. Get HPV vaccine. Wish you good health! Safe sex: https://www.hopkinsmedicine.org/health/wellness-and-prevention/safer-sex-guidelines