Welcome to HCM,
As you are regularly using coitus interuptus, you must be knowing that this method of contraception
is effective but not without failure rates.
The ejacualte around the time of your expected period, if you have regular periods, will not cause conception.
But, failures are known for this method if you had sex around the time of ovulation.
So, as you have delayed periods, better to rule out pregnancy
by doing a urine pregnancy test.
Hope this information is useful.
Dr. Mrs. Sumeet Baheti