I've always had my period every 28 days for the past nine years. I've been sexually active for the past three years, with more then one person. In the beginning of this month I had unprotected sex, a few days after my period had ended. Now, Im constantly tired, i have horrible back aches, and my period was three days late. The blood isn't a normal color, its appears black, and watery. Now I'm experiencing nausea, HORRIBLE mood swings, and some smells make me want to vomit. I even gagged while brushing my teeth today. I dont understand whats going on, I took a pregnancy test 2 days before my "expected" period, so thats 5 days before it actually came, and it came out negative. Whats going on with me?