My Gf And I Had Unprotected Sex On Friday 16

My gf and I had unprotected sex on friday 16 Dec. i used the withdrawal method and ejaculated outside. To be safe, she took Postinor 2 on 18 December. 2 tabs at once as advised by the doctor. Ever since, she has been having severe diarrhea without any spotting or bleeding occuring. What should we do? Could anyone advise the percentage of pregnancy in this case?