When Will I Get My Regular Menstrual Cycles After Taking 'levonelle'?

hi, i have taken levonelle one step within first 3 hours of having unprotected intercourse. i got my periods 2weeks earlier than usual, when will my next periods come? has levonelle altered my cycle? how long should i wait for my next periods? i have a 30 day cycle and usually get them on the 14th may, but i got it on the 1st may because of the pill. what should i do. when should my next periods come? as i havent got them and its 25th may today.