Unwanted pregnancy. In this month?

Sir/mam we have unprotected sex on 21/12/2017...after 21 hours she was take a unwanted 72...after taking unwanted 72 she have some abdominal pain and after 8 day she have bleeding and spot...this bleeding was last about 4 days...after that she don't have her menstrual period...her last periods date was 16/12/17...but in January she don't have her periods...she have her periods in 20 day per month...after missed her periods she will test 5 times with urine pregnancy test kit (prega news & quick check) but 5 time it was shows negetive...and she don't have any pregnancy symptom...so pls tell me is there any chance of pregnancy?and why she don't have her periods in this month? Iam very worried about that...I don't want pregnancy now...pls help me.