I did sex unprotected and I was expecting ma period 2 days after but no sign of it I stardet to have regular periods now but first time it don't come out I've been throwing up its already 3 weeks no period and been getting tired and getting dizzy

It oes sound like you are pregnant although the signs seem to be slightly early. You might just be coming down with an illness but try taking a HPT just in case ( take more than one because HPT are not always correct.) If you ad unprotected sex then you might have contracted an STD or an STI which could be the cause of your symptoms. I suggest talking with your GP
Stay Safe