My period is late for four days. a week ago before the period should have started i had a little bit blood, just one day and it stopped. what is wrong?

Pregnant?: If you were sexually active, first and foremost, you need to do a pregnancy test. If this is negative, than it is possible that you are having some menstrual irregularity. If it persists, see your GYN if it happens 3 months in a row.

Do a pregnancy test: If you are sexually active you may be pregnant, do a pregnancy test. If you are not pregnant it may be an irregular cycle. If this persists and you have no menses for 3 months or more and negative pregnancy tests then see your doctor for an evaluation.