You had unprotected intercourse
in the peak of the fertile period. It is good that you have taken post coital emergency birth control pills. These pills are very reliable having very good success rate. It is unlikely that you are pregnant.
However, these pills have high amount of oestrogen and progesterone
hormones which may delay the period. Also these hormones are responsible for heaviness and tenderness in the breasts.
Now that your periods are delayed by 8 days, please get urine tested for pregnancy
. By this time, it will give reliable results. If you turn out to be pregnant, you may opt for termination of pregnancy by medicines. If you are not pregnant, wait for few days and you will get menses.
I do not think there is any reason for concern.
Dr. Nishikant Shrotri