Extremely Sore, Tender and Bigger Breast But Not Pregnant

I'm 23, my last sexual relation was on the 13th and it was unprotected. My period came on the 20th, it was abnormal (light, much shorter than usual and 10 days before it was due). Since i took emergency contraception twice in the same cycle i kinda expected it to be different.
But since my breast are so incredibly sore and i'm not around my period i decided to take a quantitative pregnancy test. The result was negative (<0.1). The thing is that my breast are swollen, tender, bigger than usual, and my nipples are so sore, that even the rubbing of the nightgown or sleeping on my stomach is unbearable. What it could be?