I had unprotected sex with my boyfriend about 3 weeks ago and I wasn't supposed to get my period until the week after that day, however I got it the day after, now I was supposed to get my period 4 days ago, but no signs have showed.. could I be pregnant?

Yes.

Yes, you could.

Yes, yes you could, you will have to wait till you are 14 days late to do a pregnancy test, use first urine of the morning. * unless period comes before then