Took plan B, my period is a week and two days late. Took pregnancy test after 3 missed day, came back negative.

Can happen. Period may be delayed after using Plan B. Best to use consistent contraception to avoid such situations.
See below. I agree with the answer by Dr. Krishnamurthy in that plan B can alter menstrual cycle. You may wish to repeat the test in 4-5 days if you do not get a period by then. Use first morning urine and follow the instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex. Get HPV vaccine.