As you took I-pill within 12 hrs following unprotected sex, chance of pregnancy
is quite LESS and I-pill has more than 95% effectiveness in preventing unwanted pregnancy.
For confirmation, you can do a Home pregnancy test with urine/blood for hCG.
Other reasons for irregular delayed period are 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, blood sugar (PPBS), Blood estrogen
level etc. So consult with your gynecologist and take suggestive measures.
Avoid stress, take healthy diet Protein & IRON supplements
, control body wt and need proper sleep.
Practice safe sex in future by using condom/OCP/Em pill/Safe period etc.