What Causes Breast Pain Before A Period?

Hey doctors, y does just my right side breast hurt this month? Normally before my period both get sore then it goes away the first day my period shows up. But last month the right hurted more than the left and my cycle started 2 days early. My period isnt due for 7 more days and only my right breast hurts... around the nipple. Could i be pregnant or have cancer??