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. So you ovulated around 3rd January of this month and have low risk as he released sperm outside.
It is better to wait at least 1 wk and if period not comes, do a urine/ blood test
for hcg to confirm/ exclude pregnancy.
Other possibility of delayed period like hormonal
, ovarian cyst/ PCOD, thyroid
problem, wt gain/extreme loss, irregular eating habits etc are to be considered if pregnancy is ruled out.
Avoid stress,take healthy diets, control body wt , need proper sleep and practice safe sex in future.