is possible only,if unprotected sexual intercourse is done with ejaculation around ovulation time in regular period. Other days are low risk and varies with high failure rate.
Exclude pregnancy by doing blood test
for B-hcg & check the result. If negative,do following things.
Reasons of delayed period like hormonal
imbalance,stress/anxiety,ovarian cyst/PCOD, thyroid
problem,wt gain/extreme loss,irregular eating habits etc.
Need to investigate properly to rule out underlying pathology by USG lower abdomen,Thyroid profile,LH/FSH etc.So consult with your doctor and take suggestive measures.
Avoid stress,take healthy diet,control body wt and proper sleep with practicing safe sex in future.