Thank you for proposing your query.
I would like to explain to you here that the chances of pregnancy
are more if you have had unprotected sex between 10th and 20th day of her cycle, in view of the fact that ovulation can happen on any day in this duration. Since her Last Menstrual Period is 12th Feb and you have had sex on 17th Feb, which is the 5th day, the chances of her conceiving are Nil.
It can also be noted here, that she has taken a contraceptive
pill within 28 hrs of sex and this medication is effective if taken within 72 hrs of sex, and this also minimises the chances of pregnancy.
She has missed her periods due to Hormonal
Imbalance and not due to pregnancy. Ideally the patient should wait for a week after missing her periods, that is till 19th March. Since today is 21st march repeat urine pregnancy test again tomorrow morning using early morning urine sample, that is first urine sample of the day. If it is still negative, take her to a Gynecologist for a physical examination so that the cause for missing the periods can be excluded.