Its been a week since i had sex. my last periods where on time and 4-5days long. this time i was a day late and stopped after 2days. stress?

Could be...: It could certainly be related to stress, however the #1 reason for abnormal periods or abscence of those is pregnancy. If you have been sexually active get a pregnancy test. If negative and you are aware you have been under a lot of stress and no other symptoms wait until your next cycle and if still not normal I would suggest to see your GYN provider for evaluation.