Could I get pregnant if I had sex 8 days after my period?

Yes.

Like why though?

Because you had sex. There is no "safe" period, you can get pregnant a few days before a period, during your period, and anytime. So I don't understand why you don't? Are you very young and do not understand how you get pregnant?

Like why though?

Many women will ovulate, release an egg, midway through their cycle. A cycle starts as day one with the first day of a period and goes on until the day before the next period begins.

Your timing may be such that you could have been in the time frame to be ovulating. If you were, sperm could live for a few days waiting for an egg. If you weren't close to ovulation, or it had already passed, sperm would die off.

As Fr_Chuck stated, no time is safe, only some times are safer than others. This is because not everyone ovulates within the norm, and you can have an off ovulation. Not common, but it can occur.