Does I-pill Cause Irregular Periods?

hi i had my periods on 17 jan 2011 early morning one o clock that is at 16 one o clock in night we committed a mistake we had intercourse last night tht is 24th jan night 2 o clock he dropped inside will i get pregnant my last period before 17 jan was on 20 dec and the period which started on 17 jan i continued to bleed till 22nd jan im afraid i dont wann get pregnant if i take ipil will my periods get irregular when will i get next period if i take ipil coz next month i have booked for tirupati on 26 feb i dont want my periods to get iregular wht shal i do?????