please read!!!! late period

well ladies last week i had " sore to the touch nipples " very aggravating.. which i never get sore nipples or boobs.. well this week on Wednesday my period was supposed to start i know this because I've been keeping track of it for years. well, it didn't show.. i woke up out of my sleep Wednesday night to cramps so i was sure she was coming well got up Thursday morning and nothing! so Friday i woke up at 4:00 am to very bad pains/cramps so bad i was crying.. so i got up because I thought my period had started but again NOTHING. it is now Sunday March20th and guess what?! no period.. I really don't know what to make of this... I won't get upset if im not pregnant i just want to know what could it be?