Hello,
Welcome to ehealthforum and thanks for writing
As described by you, before the penetration protection was used and if the condom was intact and did not leak or break during the sexual act then possibility of pregnancy is nil.Unprotected intercourse always carries a risk of pregnancy and should be avoided at all.
You have also been taking contraceptive pills and if you have taken the pills regularly at the same time and the last pill was taken not more than 12 hours late then protection against pregnancy would be there.
Relax yourself as stress can delay the periods.Consider using protection everytime as it protects against pregnancy and various sexually transmitted diseases.
Take care!