Thanks for the query.
Though condom was used, if there was any accidental spillage of pre-ejaculate
fluid into vagina then we should think about the possibility of pregnancy
. If nothing happened like that then the chance of pregnancy is less.
Intercourse may not affect the menstrual cycle but stress
and strain can alter the cycle by affecting hypothalamo-pituitary-ovarian axis.
So you once go for blood test
for pregnancy which will rule out the possibility.
If comes negative you consult gynecologist and after examination go for tablets for withdrawal bleeding.