is possible only, if unprotected sexual intercourse is done with ejaculation around ovulation time in regular period. Ovulation occurs approx 14 days before due date. Though using condom has 15% failure rate whether in pull out method 15-28%.
Therefore, you need to rule out pregnancy by doing one blood test
for beta-HCG at the earliest. Early pregnancy test may give negative result.
Other reasons for delayed period are hormonal
imbalance (most common in this context), stress/ anxiety/ mental upset, irregular diet pattern, wt change, thyroid disorder
Consult with your gynecologist for relevant examination & investigation like USG pelvis, complete hormone profile etc
Avoid stress by regular deep breathing, take healthy diet with iron supplements
, keep bowel habit regular, maintain personal hygiene and take proper sleep.
Be well & take care.