I am a 16-year-old girl, and lost my virginity on 12 August.

We used a condom, which was put on before penetration, but I’m not sure it didn’t break. Even if it broke, only the pre-cum could get into me. Can I get pregnant from that?

Even the pre-cum can contain sperms. You should always check afterwards whether the condom has broken. Stress can cause your period to be late, but perhaps not that much. You can buy pregnancy tests in drugstores. It could be worth taking one, then visiting a gynaecologist, because pregnancy cannot be excluded. Hopefully, you are not pregnant. You should be very careful in the future when using condoms. You can also consider taking contraceptive pills.