If you have a history of regular periods, then this delayed period could well be a pregnancy
since you seem to have had sex during the ovulatory Unsafe Period.
A negative pregnancy test immediately after your missing the date of your period may not rule out pregnancy (although most pregnancy test kits nowadays are highly sensitive).
Repeat the urine pregnancy test with the first morning sample of urine. If it is negative wait for 2-3 days more and if still no period, repeat pregnancy test.
A delayed period may occur without a pregnancy in cases of stress
like an exam stress or in conditions like PCOS
where the release of egg is delayed or absent causing delayed, irregular periods
Hope this answers your question.