I know it's probably way too early to tell and I'll wait till my period is late before I worry but, I had unprotected sex on days 13, 15 & 17 of my cycle and for the last couple of days I've been suffering from very tender erect nipples. My period is due in about 5 days but I've never suffered any symptoms other than cramps before my periods so I don't think it's related to that.