Welcome to HCM.Pregnancy
is possible if unprotected intercourse
is done around ovulation time in regular cycle.
If you took Lo Loestrin
24 Fe on regular basis on scheduled time,then it gives up to 99% protection.
But in irregular cycle,ovulation time varies and you also took active pills during vacation instead of placebo pill.So pregnancy chance is minimal or almost nil.
Do a fresh USG pelvis to confirm or exclude pregnancy and it also rule out underlying pathology for delayed period. Take new packet of pill if not pregnant and continue on schedule basis. Consult with your doctor always.