Thanks for query.
Yes it is normal in disturbances in menstrual cycle when she is on birth control measure because they are having estrogen
and progesteron harmones and causing menstrual disturbances.
delay in period for 4day not a worry,wait for at least 10days,than go for pregnancy
test,and consult a gynae.
Chances of pregnancy in your case is nil because she is on pills and you are using condom.
so don't worry.