What Causes Delays In Menstruation?

hi my period has been bout a week late, when it was time for my period to come on i had all the regular symptons then it never came, the day before i was drinkin and the day it was suppose to come on me and my boyfriend had sex, but earlier in the month i was having relationship, financial problems and im in school. during the days my period hasnt came on my stomach has been cramping and my breasts are swollen and sore sometimes..could you give me some advice