 [ Symptoms ] what can cause a period to be late  i am 25 have always had regular periods and i am now 3 days late i had protected sex 4 days ago i have been under a lot of stress and not sleeping well could i be pregnant or what else could cause my period to be late [ Disease ] if you ve had a recent illness or you are under or over weight pregnancy pre  menopause menopause change in your meds stress are all things that can cause your period to be late