Am i pregnant?

Okay so my period started on the 13/04/14 and finished on the 19/04/14 i then had sexual intercourse on the 20/04/14 unprotected sex, we had sex around 4 times that day, which equals to 4 times he had cummed inside md. My period is now due in 4 days but this morning i woke up with very sore nipples and ive never experienced that before, and i know some of you would say its because my period is due, but i never experience this before my period, ever! they are very painful and sensitive. Could i be pregnant?