I had unpreotected sex 3 days before I was supposed to get my period, its day 6 and I still have not gotten my period

If you period is late, then you can take a test. Be sure to follow the directions carefully. If it is negative, wait another week or so and test again if still no period. If still negative, wait and see what happens when you would expect your period for next month as sometimes periods can just be off.

Becoming pregnant right before a period is unlikely, but possible, so be sure to use protection every single time you engage in sex. There is no 100% safe time as ovulation can vary a bit from woman to woman, and you can even have a one off where you ovulate outside your own norm.

I think you have to wait at least a week or 2 depending on what test you take.

While possible to become pregnant a few days before period it is not as likely ( but again can happen) you can try a test but it may be up to another two weeks to show up.