Welcome to Healthcare Magic forum.
A delay of periods for three days (as in your case)or upto a week can occur due to any physiological stress
to the body be it illness like typhoid
or the antibiotics analgesics used for it's treatment.
It is highly unlikely for sperms to pass into vagina without genital contact, and through layers of clothes .However it can't be considered impossible for a female to get pregnant by unprotected intercourse
even if it's 7 days before ovulation since the sperms can remain viable in female genital tract for 3_5 days.Also the exact day of ovulation can't be predetermined and won't necessarily be fixed.
So I would advise you to get a urine pregnancy
test done if your periods do not come by another week or so.
Please do not worry as stress will further delay the periods.
Most likely you are going to get your periods within a week as chances of pregnancy are remote or negligible.
Wishing you all the best