About a month ago I had protected sex (condom and Im on the birth control pill. A day after I had sex, I bled for four days straight like a period. Even though I wasn't supposed to get my period until a week later. Now, my nipples are extremely sore, I'm having cramps, and my breasts are extremely veiny. Even though i'm not due to get my period for another few days, I took two tests and they came back  negative. What could these symptoms be from?