Hi! I Had A Sexual Activity About 4 Days Ago.

Hi! I had a sexual activity about 4 days ago. And about to have my period on the 16th. I went to my OB yesterday and she advised me to take duphaston for 5 days. I would like to ask fora further information on why did my OB asked me to take duphaston. Is it a sign that I am pregnant? Or she just want to fasten my period? When can I expect my period after finishing taking this med for 5 days.

Please help