Sore nipples

So my nipples have been really tender and sore to touch for the past week and I don't know why. I haven't had my period since may 5th I'm a little late and I have had sex with a condom, so I don't know if they are sore because my period may start or if possibly I'm pregnant? I've had sore breast before starting my period before but now it's my nipples, anyone have any idea?